GB2274716A - Circuit tester - Google Patents

Abstract

A universal circuit tester rest box (1) comprises a housing for receiving a demountable setting up module (Figure 6) whereby an output from a signal generator and/or a power supply is fed to a unit under test (9a) in accordance with a predetermined connection requirement. The setting up module comprises a printed circuit board providing for the pre-configuration of the desired conducting paths and varies from one unit under test to another. A digital multi-meter monitors responses from the unit under test. <IMAGE>

Description

TEST UNIT This invention relates to an electronic test box. It is apparatus intended for manual functional testing of electronic equipment and circuits, fault finding of such equipment and for use in their design and development.

The testing of electronic equipment often involves making in house 'Test Boxes' for each new product that a company develops. These are usually time consuming and expensive to build - all are generally 'one offs'. They often require a number of external instruments - power supply (PSU), DMM (Digital Multimeter), signal generator etc in order to perform a full functional test on a piece of electronic or electrical equipment. Gathering and setting up all this equipment (and making it work) can take a long time.

The invention described herein is designed to overcome many of these problems and make the testing of electronic equipment much easier and quicker, especially where a range of different units have to be tested frequently.

According to the present invention there is provided a universal test box comprising a housing incorporating or providing support for: (1) a signal generator; (2) a power supply; (3) regulating means for selecting output from the signal generator and/or the power supply; (4) output means whereby output from the regulating means can be supplied from the box to a unit under test; (5) a monitor for signals generated by a unit under test; and (6) a demountable setting up module whereby output from the signal generator and/or the power supply is fed to the regulating means in accordance with a predetermined connection requirement.

According to a first preferred version of the present invention there are provided input means to receive a signal from a unit under test and to feed the signal or a derivative thereof by way of a path in the setting up module to the monitor According to a second preferred version of the present inverntion or the first preferred vertsion thereof the setting up module comprises a printed circuit board providing for the pre-configuration of conducting paths between the generator and/or the power supply and the regulating means.

According to a third preferred version of the present invention or the preceding preferred versions thereof at least one of the signal generator, power supply, regulating means and monitor are of modular form.

According to a fourth preferred version of the present invention or any preceding preferred version thereof the regulating means incorporates a control panel having a plurality of switches and a plurality of visual displays. Typically the control panel includes means for controlling the level, amplitude or other function of an output of the signal generator and/or the power supply.

According to a further version of the fourth preferred version the control panel is provided with at least one demountable panel overlay for location in a predetermined position on the control panel; the overlay having regions thereon indicating the function of some or all of the switches and/or some or all of the visual displays in dependence on the predetermined connection requirement.

According to a fifth preferred version of the present invention or any preceding preferred version thereof the there is provided at least one expansion bus whereby additional demountable modules can be added to the universal test box.

According to a sixth preferred version of the present invention or any preceding preferred version thereof ther is provided a demountable pre-set module whereby a selected one of a plurality of signal generator outputs, each output providing or deriving a predetermined level of signal output from the signal generator, can be fed to the regulating means. Typically the pre-set module is provided with at least two switches and at least one demountable panel overlay adapted for location in a predetermined location on the pre-set module; the overlay having regions thereon indicating the functions of some or all of the switches.

According to a seventh preferred version of the present invention or any preceding preferred version thereof the monitor comprises or incorporates a digital multimeter.

Hereafter the universal test box of the present invention is referred to as the 'UTB'.

A major feature is the provision of a setting up module for a universal test box. This feature means that the UTB can be easily reused many times for different products.

Reconfiguring instruments by plugging in a module of some sort is not new (eg plugging a software cartridge into an instrument). The idea of a universal test box is not new but the present invention provides for the use of a setting up module which makes the UTB readily adaptable by plugging in a different setting up module as appropriate to set up the 'hardware signals'. In particular the present invention provides for the presetting of a signal generator to give three (or more) preset-up waveforms. Achieving such features with software cartridges and computer memory is not new on much more advanced signal generators. However this is an expensive path to follow and the present invention provides a UTB allowing for the presetting of the required 'hardware'.

It is readily used for testing electronic/ electrical items - boards, assemblies full products etc - by simulating their real application (as far as possible). The UTB provides input stimuli to the unit's inputs by switches, signal generators etc, and simulated or 'dummy' loads to the unit's outputs, and allows monitoring of these using lamps and a DMM (Digital Multimeter). Correct operation of the unit can be verified by visually monitoring the unit's responses to these input stimuli.

To test a unit, the test operator would normally go through a TEST PROCEDURE, and for each step of the test procedure he or she would select the switches, signal generator settings and so on, and check for the correct outputs from the Unit Under Test (UUT) and check its performance. When all the steps had been passed, the unit would be then deemed as having passed the test.

In particular the UTB serves to fill a gap in the market between complex computer controlled Automatic Test Equipment (ATE) systems and basic 'home made' test boxes, which are only used for the one product. The ATE systems are not cost effective for testing small volume products and these systems are expensive - usually over 20,000 and often a lot more. The jigs and reprogramming needed for each new product are also expensive frequently comparable in price to a test box according to the present invention.

The UTB is particularly useful for companies who have to test low volumes of a wide variety of different products. In such situations Automatic Test Equipment is not feasible.

Other adaptable test boxes are available, but they are aimed at one particular field (for example radio communications or cable testing) and are often intended for making complex and very accurate measurements. These also tend to be very expensive - eg.

over 12,000 for a radio communications tester. The estimated selling price of the UTB described hereafter is around 1000.

The invention described has many uses and it is aimed primarily at electronic equipment testing and fault finding. It has other applications including use as a tool for electronic design and development - it will be invaluable with its built in PSU and DMM, switches and lamps. It is very handy for quickly trying out new circuits during development work In addition a special UUT to TEST BOX cable will be available with terminal blocks (or similar) on the end, which will allow users to quickly connect up their development circuits to the UTB's switches etc. This will save them having to make up a new cable to quickly try out a circuit.

It is very useful as a general purpose bench instrument - all the features (DMM etc) are available via their own terminals/ connectors. It can have uses in product proving and performance testing of high volume products, for example, where products need to be exercised fully while in test chambers, and this testing is usually done well before the production ATE equipment is available.

It will be very useful to service engineers and technicians, as it is intended to be portable and a sturdy carrying case will be available along with a battery power supply (external) to run the UTB for use in the field.

It could have applications as a teaching aid for schools, colleges etc. It could also be useful for companies demonstrating their products. The UTB is readily manufactured to be smart and professional looking so providing a more efficient appearance than 'home made' test boxes, especially for demonstrating products to potential customers.

The UTB is designed to save users time and money on their manual testing of electronic or electrical products. It is designed to replace all their test boxes and associated test instruments with one easy to set up and very versatile UTB.

A UTB can dramatically reduce the time taken to set up and carry out the required testing - particularly reduce the time taken to collect all the equipment and connect it all up, and set it up - and make it all work. The UTB has all this in one box that is very quick to set up.

One of the major features of a UTB is the ease with which it can be reconfigured to test a wide variety of different products - quickly and easily. All you do is plug in a setting up module, put on another panel overlay, plug in the product interface cable, switch on and you are ready to start testing in less than a minute. The built in Power supply, and DMM make collecting, finding, connecting up all the equipment a thing of the past. The Signal generator further helps for more complex products. The Signal Generator has a function generator with a built in frequency meter, DC voltage drivers and a 4-20mA current source. In addition the function generator part of the signal generator has its own 'PRESET Module' that can be used to set up to three 'PRESET' signals that can be accessed via a switch on the signal generator.This can save a lot of time in setting up the system ready for testing and for where more than one waveform is required - up to three waveforms can be preset on each PRESET Module.

See later for full description of this.

Users no longer have to make a new test box for each new product. They can use the same UTB for each one. They simply set up a new setting up module and make up an interface cable to their product and put some lettering on a new panel overlay, and they have a new test box, in a fraction of the time it would have taken to build one from scratch.

Designing and building an interface to test a new product is straightforward. Decide the signals you require into your Unit Under Test (UUT) and which outputs you wish to monitor; and decide which switches and lamps etc to use for these; Put some lettering on a new panel overlay so you will know which switch and lamp does what.

Configure the links on the setting up Module to suit this, including any links for DMM channels and signal generator etc. Make up an interface cable to go from the UTB to your UUT. Plug in the Setting up Module, the interface cable and your UUT, and put on the new panel overlay and you are ready to start testing.

The UTB is essentially of simple and straightforward design, consisting mainly of interconnections, and is designed to be very easy to repair (often by the users), should anything go wrong. In addition the major parts are modular and can be easily changed - eg the PSU. Even with the best intentions, test equipment can (and often does) get damaged during testing - eg due to a very faulty UUT - putting mains on a 5V line, for instance, so ease of repairing the TEST BOX is very important.

The UTB has built into one box, a number of switches, signal generators, and a power supply (PSU) to provide input signals to the Unit Under Test (TUT) and numerous LEDs, lamps and a DMM (Digital Multimeter) to monitor the UUT's outputs. These are all easily configurable via the plug in 'Setting up Module' to enable different items to be tested. The UUT plugs into the UTB via an interface cable.

A specific embodiment of the invention will now be described by way of an example, with reference to the following drawings of a UTB of which: Figure 1 is a front view of control panels; Figure 2 is a front view of a main control panel; Figure 3 is a front view of an auxiliary control panel; Figure 4 is a front view of a top panel; Figure 5 is a front view of a rear panel; Figure 6 is a block diagram; Figure 7 is a perspective view of a setting up module; Figure 8 is a layout diagram of the setting up module; Figure 9 is an example of a switch configuration; Figure 10 is an example of a lamp configuration; Figure 11 is of an interconnection circuit; Figure 12 is a layout diagram of a preset module; Figure 13 is a perspective view of the preset module of Figure 12; and Figure 14 is a top view of the preset module of Figure 13.

FIGURE 1 This shows the various panels of the UTB and the case. The UTB 1 consists of a case 2 with two front panels - one Main Controls panel 3, and one Aux (auxiliary) Controls panel 4; a top 5; rear panel 6; and two side panels 7 and 8. On the right side of the case is shown is the 'Expansion Bus' connector 9. This will be referred to later. There is another Expansion Bus connector on the other side panel 7. Also shown is a Unit Under Test 9a (UUT), with its interface cable 9b.

FIGURE 2 This shows the Main Controls panel. These are the controls that are used to apply the stimuli and monitor the responses from the Unit Under Test (UUT). There are twelve toggle switches 10, four push button switches 11; Two rotary switches 12; and two potentiometers 13. There are twelve LEDs mounted above the switches 14, and eight further LEDs mounted on the left in a row 15. There are four bulbs (12V nominally) with coloured holders 16. There is some spare space 17, on the front panel to allow users to add extra controls if required - see later 'Advanced Configuration'.

The Main controls Panel 3, comes supplied with some transparent panel overlays which can be put onto the front panel. The markings and functions of each switch etc can then be written on the panel overlay for ease of use. Each different product to be tested will have a different panel overlay, as the box configuration will be different for each one. This greatly assists the users in testing different products.

FIGURE 3 This shows the Auxiliary Controls panel. This contains the controls for the PSU, Signal Generator, and DMM. The Power Supply Unit (PSU) 20 features four power rails, +5V, -5V, +12V (for example) and a variable rail 0 to 24V with adjustable current limit.

All the rails are fully protected. The +5 and -5V rails are turned on/off by switch 21.

The +12V rail is turned on/off by switch 22. The Variable power rail is turned on/off by switch 23. The LEDs 24, 25, 26, provide indication that the relevant rail is on and OK. The voltage of the Variable rail is adjusted by potentiometer 27, and the output current limit is set by potentiometer 28. When the supply is 'current limiting', LED 29 lights to indicate this.

The Signal Generator 30, has two main parts - a DC signal generator and a function generator. The DC generator has two voltage sources and one DC current source which provide a smooth low impedance adjustable signal. The range is determined by the Setting up - ie which PSU rails it is connected to. Typically +/-5V. The DC1 voltage source has a on/off switch 31, an 'on' indicator 32, and a 10 turn adjustment potentiometer 33. This allows precise setting of the output. A test point 34, allows for direct independent checking of this voltage. Voltage source DC2 below the above is the same except it has a single turn potentiometer 35.

The DC Current source provides 4-20mA or 0-25mA current signals. These signals are used a lot in control applications for sending data and measurements from sensors to instruments etc. It and has an on/off switch 36 and 'on' indicator 37, a mode select switch 38. This determines whether the DC source is operating digitally high (20mA), digitally Low (4mA), or variable. The range of the variable output is set by switch 39, and selects either 4-20mA or 0-25mA (for checking over range operation on instruments etc). The variable level is adjusted by the 10 turn potentiometer 40.

The FUNCTION GENERATOR is based on an adjustable waveform generator. It provides the following outputs - Sine wave or Triangle wave, and a square wave. The Square wave output is available separately to the sine/ triangle wave. The function generator can be preset for three different outputs with the amplitude and frequency all presentable on a plug in module. This is achieved by plugging in a Signal Generator 'PRESET Module' into the UTB. A different PRESET module can be plugged in to give three more preset waveforms. Rotary switch 49 selects which of these three preset channels is used, or selects NORMAL mode in which the controls described below work'as normal'. This feature saves the users much time when performing tests, and when setting up initially. The Signal Generator Setting up Module and its adjustments are described fully later.The following description refers to NORMAL mode.

The outputs are adjustable over a wide range, typically .001Hz to 10MHz in three ranges. Push buttons 50 select the range, and potentiometers 51, 52 allow Course and Fine adjustment (respectively) of the frequency. Frequency meter 53 shows the output frequency on a digital display. Switch 54 selects either sine or triangle wave output.

Switch 55 selects whether the Square wave output mark:space ratio is 1:1, or adjustable by means of potentiometer 56. The amplitude of the triangle or sine wave signal is adjustable, by potentiometer 57. Output indicator LED 58 flashes with the square wave output and shows that the output is active and OK. It is especially useful at low frequencies as it can be seen flashing at the output frequency. Switch 59 turns the function generator on/off with 'on' indicator 60.

DIGITAL MULTIMETER (DMM) consists of a digital display 70, Push buttons for on/off, display Hold and display illumination 71,72,73 respectively. The Multimeter is 'autoranging' over four ranges and can measure ac, dc voltage, dc current and resistance. The DMM function is selected by a six position rotary switch 74, for Volts ac, Volts dc, Ohms High, Ohms Low (with a continuity beeper), and current High and current Low. The channel switch 75 selects which input goes to the DMM. Most of these channels will be used to measure dc voltages. This is from either of the four PSU rails, or External - ie for use as a normal Bench Multimeter, or from one of six measurement channels. These measurement channels are configured using the main Setting up module and allow easy monitoring of UUT output levels by simply turning this control.

Typically circuitry is provided whereby the DMM can display the frequency of the Signal generator output. This will save having a separate frequency meter. A further embodiment can include a means for measuring PSU and channel currents via the channel switch, and also to display the current limit setting of the VARiable PSU rail.

The DMM can also measure directly the current from the 4 - 20 mA DC current source and the voltage of the DC voltage sources, on the signal generator.

Additionally, a more advanced embodiment provides a means whereby the DMM function is set up via the channel switch. That is for each channel setting, the DMM can be setup to read the required function - eg. read DC Volts with respect to ground on channel 1, and read DC Current in the UUT supply on channel 2, and so on.

The DIGITAL MULTIMETER has further controls mounted on the top panel of the case 5. This makes it easy to use the external test leads without interfering with the main control panels. With reference to FIGURE 4, these are the input connections for the External DMM channel. There is a red socket 80, for Voltage and resistance measurements; a black socket 81, for the COMMON input; a yellow socket 82, for the low current input (up to 40mA); a white socket 83, for the high current input (up to 4A). These sockets would all be shrouded 4mm sockets In addition there is a fuse and holder 84, to protect the current input. There is a very useful switch 85, which selects whether the DMM common input is connected to system ground (0V) or to the COMMON input socket. This saves having to always manually connect the DMM COMMON input to ground.Nearly all measurements made are with respect to ground. For other measurements eg external current measuring, the switch 85 can be set to the COMMON socket and this line connected up as required.

FIGURE 5 This shows the REAR PANEL which contains most of the connectors for the UTB. The main connectors to the Unit Under Test (UUT) are P1 and P2, 90,91. The interface cable (9b) to the UUT plugs into here. Generally a different interface cable will be used for each different UUT, unless they have the same connectors and similar pin outs etc.

These are typically a 48way and 28way connector respectively. P1 handles all the main switches and LED signals along with the PSU rails. P2 handles the other signals Signal generator outputs, DMM channel inputs, Pots and rotary switches etc. If real loads are required to be included as part of the test jig eg motors, solenoids etc, then these can be incorporated as part of the interface cable between the TEST BOX and the UUT. The output lines form the UUT would go to the real load, and the same line would also go to the TEST BOX for monitoring on the DMM and LEDs, if required.

These real loads could be built into their own box, if desired.

The Setting up Module plugs into connector P3, 92. A different Setting up module is plugged in for each different item to be tested (unless they are simple and/or very similar). This is typically a 96 way connector. The PSU outputs are available on five terminal posts 93, for easy connection of wires up to the built in PSU - eg for use in circuit development, or as a bench instrument.

If a UUT requires more current (or voltage) than is available from the built in PSU, then a suitable external PSU can be connected to these terminals. The relevant rail should be turned off on the PSU panel (switch 21,22 or 23), and the external PSU will now power the required TEST BOX rail as normal. A typical maximum rating of the TEST BOX for an external PSU may be 60V, 13A. Mains ac (eg 240V at up to 13A) input via these terminals for the UUT maybe possible, depending upon the relevant electrical safety regulations.

Below these terminal posts are the connectors for the signal generator outputs for use when the UTB is being used as a bench instrument eg for circuit development. All the these and the PSU rails are also available directly to the UUT via P1 and P2. There are typically three 4mm sockets 94 for the DC1, DC2 and DC Current outputs; and two BNC sockets 95, for the Triangle/ sine and square wave outputs. P7, 96 is the connector for the PRESET module for the signal generator preset waveform outputs.

This gives three preset waveforms from the UTB.

Along the bottom of the rear panel are the mains input connector 96, with a fuse built into it; illuminated mains on/off switch 97, switched mains outlet connector 98 (for use with other equipment eg oscilloscope that can be conveniently turned on/off by the UTB's on/off switch). Next to this is the external battery power input connector 99, typically a 3 way XLR socket. When under mains power smoothed unregulated low voltage dc is available on here from the built in PSU (typically +25V, -9V dc at up to 6A, 1A respectively). This can be used by the users or to charge up the external battery pack when it is connected.

On each side of the UTB are located Expansion Bus connectors 9 (Figure 1), typically 15 way. These are used to plug in a special Expansion box that has typically eight more switches and Lamps, one rotary switch, and one potentiometer, for use when there are not sufficient on the main front panel 3. There is a means of securing these boxes onto the UTB to prevent the connector coming out by mistake.

In addition a special 'USER BOX' can be plugged into the Expansion Bus. A USER BOX is basically a bare box with a plain front panel, and only the Expansion Bus connector on the side. It is utilised by users to make up their own special circuits with the required controls etc all built into this USER BOX, for use in their testing with the UTB.

The Expansion connector provides the five PSU rails (inc ground) and has five lines that go to the Setting up module - and can go direct from here to the UUT, depending on the configuration. The remaining five lines are available on the main front panel PCB for Advanced Configuration (see later).

FIGURE 6 This shows a block diagram of the UTB system, with the Setting up module at the heart of it. The Setting up module will now be described in detail.

Setting up MODULE In a conventional test box that can only test one item, all the lines from the switches and LEDs etc would go to the UUT. The signals to the switches and power feeds for the LEDs etc would be 'hard wired' onto the switches and LEDs. In this reconfigurable test box invention the 'hard wired' part is replaced by a Setting up Module. This allows the Setting up of all the switches etc to be changed for each different UUT. The lines from the switches and to the lamps go directly to the UUT, as with a normal test box.

The Setting up Module 100, forms the heart of the UTB invention. It is a small box that plugs into the rear panel 6, of the UTB, into the Setting up connector 92. Each different item to be tested will have its own Setting up Module (unless the items are very similar).

FIGURE 7 This shows a drawing of the Setting up module, 100. It consists of a small box 101, with a removable lid 102. The connector 103, is on the front and this plugs into the UTB. Inside the Setting up module is a PCB with many links and holes to allow the required configuration to be connected up. The PCB is removable to assist with the configuring.

The Setting up Module 100, is essentially a means of connecting various pins on the Connector 103, together. The Setting up Module has a line from all the switches and most of the Lamps. These lines are provides with holes in the PCB to allow for wires to be attached to configure these lines - ie connect them to the required signal. These lines are typically on the component (top) side of the PCB. Many of these also have links for quick configuration, typically the 0.1" moveable link type. Many connections are already 'MADE' by 'DEFAULT on the Setting up Module as these connections are used often (see Figure 11 and later), and these save the user time when configuring new Setting up modules. We will refer to this as DEFAULT Configuration. Such connections can be easily removed by cutting the relevant 'EASY CUT track, and the line reconfigured as required.Special track cutting places are provided.

FIGURE 8 This shows the Setting up module PCB 104, with the links 105, and some of the tracks 106, with holes 107. The power rails run up the Setting up Module on tracks 108, with plenty of holes 107 (with solder pads) to allow connections to be made easily. These tracks are typically on the solder side (under side) of the PCB. The majority of connections on the Setting up Module are to the power rails or to ground.

A basic function of the Setting up Module is to give signals to the switches - often from the power rails - for applying to the UUT when the switches are operated. The Setting up module determines the power rail feeds to the LEDs and bulbs on the main panel. For example some products will need the feeds to be from +12V (ie the UUT provides an active low output -pulls its output to ground), whereas others will need the feed to be ground (ie the UUT provides an 'active high output'). The feeds to the potentiometers and rotary switches are also configured on the Setting up Module.

The Setting up Module also has a small space 110, for users to build up small circuits for more complex applications. Many holes 107, with solder pads are provided on a .1" grid spacing for this purpose.

Further functions of the Setting up module will be described now with reference to diagrams and examples.

FIGURE 9 This shows the configuration circuit for one switch. Each switch 110, has a link 111, associated with it on the Setting up module. This is connected to the switch's Normally Open (NO) contact, and allows quick connection of the NO contact to either Ground or a Power rail. The example shown has this line linked to +V. The power rail +V (eg +12V) that is on these links is determined by a wire link 109 (Figure 8) and this sets all the switch links to this signal. If the switch needs a different power rail (or signal) to the others then it can be easily be connected by a wire link to the switch NO line. This circuit also shows a resistor 112, as an example, connected to the NC (Normally closed contact) line of the switch This may be needed sometimes to give a pull down OFF signal to the UUT - eg for driving analogue inputs.The circuit 113 shows clearly the circuit that the above example has shown.

If the actual line to the UUT (ie from the wiper of the switch) needs a pull down resistor, for example, this can be achieved by connecting the switch output line on the UUT interface cable to a SPARE line on the UUT connector, and a suitable resistor added in the Setting up Module from this line to the required rail. This is shown in the circuit 114, with line 114 shown as providing the required resistor 114b, to ground (in this case). This arrangement is useful for developing circuits with 'raw CMOS' inputs for example. Finished products would normally have some form of input resistors.

FIGURE 10 This shows the configuration for a bulb and an LED. The LED 115, and its resistor 117, is fully configurable on the Setting up module. This means that it can have its polarity swapped as required, by reconnecting it the other way round - as shown by LED 118, with its resistor 119, connected to ground. The LED resistor is put on by the user to suit the voltages being used. The bulbs 116, are connected direct to the required supply rail. No resistor is needed for these. Their working voltage is typically +12V, but this can be altered either by adding a resistor as per the LEDs, or by changing the bulbs (eg to +5V bulbs) by removing the lamp holder cover on the front panel.

LED 115 can be configured by DEFAULT to be the way round shown, by means of an EASY CUT track 120, as mentioned earlier. Most LEDs etc are driven from the 'low side'. To alter this to be like LED 118, the user would cut this track and reconnect the lines as shown.

The DMM channel lines are provided with EASY CUT tracks. By DEFAULT the DMM channels are connected directly to lines from the UUT. This enables the lines to the UUT to be reused for other means on the Setting up Module if the DMM channel(s) is not required. In addition, the DMM channels can be connected to other signals on the Setting up module. Eg to measure an output voltage to an LED. This is shown by link 121 on Figure 10, where the output from the UUT is also fed to a DMM channel for voltage measurements. Note that this is not possible on all output lines as not all the signals come directly onto the Setting up module (eg on bulb line like 116). To connect these simply add an extra wire on the UUT interface cable to a DMM channel line.

Two rotary switches 12 (see Figure 11) are also configured via the Setting up Module.

The first switch has all its ways (6 + wiper) available on the Setting up module. All the ways are connected by DEFAULT configuration to the UUT. They can also be connected within the Setting up Module as required - eg via different resistors to Ground to give a range of resistances from the switch. The wiper is configured in the same way as a normal switch, by a link. The second switch has all six ways going direct to the UUT, with the wiper coming on to the Setting up Module as for normal switches.

The two Potentiometers 13, are connected in a similar manner. The first is connected fully through the Setting up Module, by DEFAULT Configuration to the UUT. The second has all signals going direct to the UUT.

The power supplies for the signal generators are also set up on the Setting up Module.

This allows the supply rails to be chosen to give the required voltage range to suit the UUT. For example some products may need signals in the range -5V to +5V, whereas others may need 0 to 20V.

All the outputs from the signal generators are fed into the Setting up Module for connecting up as required. These lines also go directly to the UUT. Additionally the lines to/from the Expansion Bus are available on the Setting up Module. This could enable, for example a signal from a user box (eg a special analogue signal) to be connected via one of the main switches to the UUT.

FIGURE 11 This shows a full interconnections circuit of the UTB. With reference to figure 11, the lines shown 130, within the Setting up Module 100, are for DEFAULT Configuration.

The dashed lines 131 indicate an example of configuration for the switches and LEDs etc, utilising the 0V and +12V rails in this example. Also shown are some example components used in the configuration - resistors, 132.

In order to fit all the features onto the Setting up Module and using a single 96 way connector, as proposed in this embodiment of the invention, it is required to restrict the number of signals onto the Setting up Module. Two examples of this limiting are LEDs can be commoned into groups of four, with just the supply line to each group being Setting up. The polarity and resistors can be altered by advanced configuration (see later). Some of the LEDs - typically four - can still be fully configurable via Setting up, as was shown in figure 10. The rotary switches and potentiometers could have only one of each fully configurable on the Setting up Module (as described earlier), in addition some of the lines from the rotary switch on the Setting up Module could be left unconnected by DEFAULT.These lines can be then connected to the UUT by using another unused DEFAULT connection (eg using an unused DMM channel line to the UUT).

The main reason for having many of these lines coming into the Setting up Module, and then sent out again via DEFAULT Configuration, is to allow these lines to have resistors (for example) added onto them, or for the lines to the UUT to be reused for other purposes as required.

FIGURE 12 This shows a circuit of the PRESET Module that is used to 'remember' waveforms for easy setting up of the instrument for future use. The Preset Module is housed in a small box similar to the Setting up Module, and plugs into the rear (into connector 96) of the UTB.

FIGURE 13 This shows the Preset Module 140, its box 149, with connector 150, and top 151. The Preset Module has a number of small 'preset' potentiometers (pots) and slide switches on it, and these are available to the user via cutouts in the top of the box.

FIGURE 14 These potentiometers are on the top of the box 151, with pots 143, 144, and slide switches 141, 142.

The pots are adjusted using a 'pot twiddler' tool. The users set up their required waveforms using the potentiometers and the small slide switches. Up to three waveforms can be set up on each Preset Module. These Preset Modules would be used in the same way as the main Setting up Modules - that is a different one could be used for each different item to be tested. This makes setting up the instrument very quick and efficient, further saving valuable test time. The signal generator can of course be still used as normal.

With reference to FIGURE 12, the Preset Module 140, has about 17 connections to the signal generator. The Preset Channel select switch 49 is typically a 4 pole switch with 4 ways - Normal, Preset 1,2,3; shown on figure 12 as N,1,2,3. This connects the relevant pots and switches into the circuit depending on the channel selected.

The function (sine or triangle wave) is set on the Preset Module by switches 141 (one for each Preset channel). Switch 54 selects this for Normal operation. The range is set on the Module by switches 142. Switch 50 sets the range for normal mode. Again, switch 49 determines which of these switches is in circuit, and hence selects the channel. The frequency is Preset by the 10 turn preset pots 143 - one for each channel.

In Normal mode, the frequency is adjusted by pots 51 and 52 (course and fine). Single turn preset pots 144 adjust the output amplitude of the sine/triangle wave signal. Pot 57 adjusts this in normal mode. The mark/ space ratio of the square wave output can also be preset for each channel by a similar means, should this be desired -this is not detailed here.

ADVANCED CONFIGURATION Advanced configuration involves customising the UTB to suit a users exact requirements. This is not intended to be altered for each new product to be tested, but is more for setting up initially for the users general requirements or to suit a particularly complex application. Examples of this include altering the polarity of some of the groups of LEDs, and changing their resistors to suit different voltages. This can easily be achieved using EASY CUT tracks and EASY ADD Links on the main front panel pcb, similar to those on the Setting up Module. In addition circuits may be built onto the main panel PCB using the hole grid provided (like that on the Setting up Module), along with extra front panel controls using the spare front panel space (17).

The spare lines from the Expansion bus (typically 5) are available on the main front panel pcb for connecting up as required via Advanced configuration.

Another feature that can be available by advanced configuration is to have some 'DEBOUNCE' circuitry available on the main front panel pcb. This would enable some of the switches to be connected to the UUT via a 'debounce circuit'. This is very useful for driving CMOS flip flop inputs and the like, where switch bounce can cause false operation of the unit. Switch bounce is where the UUT 'sees' many transitions from the switch for one operation.

OTHER FORMS OF THE INVENTION Many embodiments of a test box according to the present invention are possible. A lower cost version than that described above typically contains all the features as described saving the signal generator. The signal generator (as described) could be available as a plug in module and would connect into the side of the UTB via an Expansion Bus connector to get its power and output its outputs.

More basic models can be made available, for less cost, with less features. Such an example might typically contain the following features: 8 switches and 8 LEDs, one rotary switch and one pot; PSU, +12V (or optionally +5V), mains powered; No DMM, or signal generators.

These units would still have the Setting up Module feature.

A 'base model' can be provided without the PSU. In addition this unit could also be used as an expansion box for a main test box, for use when extra switches etc are required, as described earlier. A further lower cost model can be provided without the demountable setting up module. In this version the features found in the demountable setting up module (movable links and wire links and so on) are provided inside the further lowere cost model. This model is set up in the same way as was the case with the demountable setting up module described earlier. The further model is retained in this configuration for testing a given product until it is reconfigured for a fresh product.

Conversely, more complex models can be built containing more features. For example a bench mounted system (that is to say one which is not portable) that contains a more powerful PSU, a more elaborate Signal Generator etc. This system can also contain an oscilloscope for more advanced testing and fault finding. The construction could be modular and based on 19" racks to enable the easy interchanging of modules for different testing applications and maintenance etc. Different modules could be fitted depending on the testing required.

If required a given embodiment of the invention, particularly a smaller version, could have a terminal block on the back to help users connect up wires quickly for development work etc - in a similar manner to that described earlier for the TEST BOX to terminal block special cable.

Another special interface that could be available for the invention is a TEST BOX to 'Breadboard' assembly. This would have a breadboard (or prototype board) on the end of a short cable from the UUT Connectors on the TEST BOX, for users to quickly build up development circuits, and easily interface them to the UTB. Alternatively a breadboard could be available as an option to fit on the spare space on the front panel (17), and connect directly to the front panel pcb.

The invention could be taken a step further to turn it into a simple ATE (Automatic Test Equipment) system. This could be achieved by connecting up a reed relay switching unit to the front panel (or to the Setting up Module). This would enable the switch signals to be operated by the relays under the control of a simple computerised sequencer - eg by a PLC (Programmable logic controller) or a Personal Computer (PC).

This would automatically provide the stimuli to the UUT, instead of a user having to manually operate the switches. In addition a programmable DMM could be used in place of the normal DMM. This DMM would be connected to the PLC/PC to log the results and check them. If the DMM channel selection is done by reed relays - again under the control of the PLC - then a means for automatically monitoring the UUTs outputs can be provided. This would create a simple Automatic Test System, that could be easily reconfigured as per normal, and a different PLC programme used to test different products.

Another partly Automatic system can be utilised whereby the DMM is replaced by a Programmable DMM, as above. This could be connected to a PC, and the PC could log the results for each step of a test, and check that the results are OK. The PC could prompt the user to apply a specific test pattern via the switches. This would form a 'computerised test procedure'. The user would then apply the stimuli via the switches etc, press a button (for instance) to signal to the PC to start measuring, the DMM would then take all its readings (with the user operating the channel switch as required), and the PC would check the results. At the end of the test it would be the PC that determines whether a unit has passed or not.This method could improve the quality of the testing, and allow less potential for operator error and does not allow any tests to be skipped, and hence reduce the likelihood of faulty units being passed.

A simpler version of the 'Computerised test procedure' that can be used with the invention as described, could have the PC prompting for test pattern sequences, as described above, but the user would measure the results manually using the DMM etc, and type these into the PC. The PC would then determine if the results are OK.

Another related PC based feature could be a program to assist users with configuring the UTB for testing a new product. Users would enter their requirements - switch functions, and UUT connections etc. The program would then create a connections list and a specification for the TEST BOX to UUT Interface cable (9b), and also create a list and diagram of the required links etc to be added to the Setting up Module. Any advanced configuration details could be described as well. A circuit diagram of the TEST BOX and the interface could be created by the program. A panel overlay could be also created by the program along with labels etc for the Setting up Module. This could greatly assist users in performing the reconfiguration, particularly if they are unfamiliar with the UTB.

Claims (12)

1 A universal test box comprising a housing incorporating or providing support for: (1) a signal generator; (2) a power supply; (3) regulating means for selecting output from the signal generator and/or the power supply; (4) output means whereby output from the regulating means can be supplied from the box to a unit under test; (5) a monitor for signals generated by a unit under test; and (6) a demountable setting up module whereby output from the signal generator and/or the power supply is fed to the regulating means in accordance with a predetermined connection requirement.

2 A universal test box as claimed in Claim 1 including input means to receive a signal from a unit under test and to feed the signal or a derivative thereof by way of a path in the setting up module to the monitor

3 A universal test box as claimed in Claim 1 or Claim 2 in which the setting up module comprises a printed circuit board providing for the pre-configuration of conducting paths between the generator and/or the power supply and the regulating means.

4 A universal test box as claimed in any preceding claim wherein at least one of the signal generator, power supply, regulating means and monitor are of modular form.

5 A universal test box as claimed in any preceding claim wherein the regulating means incorporates a control panel having a plurality of switches and a plurality of visual displays.

6 A universal test box as claimed in Claim 5 wherein the control panel includes means for controlling the level, amplitude or other function of an output of the signal generator and/or the power supply.

7 A universal test box as claimed in Claim 5 or Claim 6 wherein the control panel is provided with at least one demountable panel overlay for location in a predetermined position on the control panel; the overlay having regions thereon indicating the function of some or all of the switches and/ or some or all of the visual displays in dependence on the predetermined connection requirement.

8 A universal test box as claimed in any preceding claim equipped with at least one expansion bus whereby additional demountable modules can be added to the universal test box.

9 A universal test box as claimed in any preceding claim including a demountable pre-set module whereby a selected one of a plurality of signal generator outputs, each output providing or deriving a predetermined level of signal output from the signal generator, can be fed to the regulating means.

10 A universal test box as claimed in Claim 9 wherein the pre-set module is provided with at least two switches and at least one demountable panel overlay adapted for location in a predetermined location on the pre-set module; the overlay having regions thereon indicating the functions of some or all of the switches.

11 A universal test box as claimed in any preceding claim wherein the monitor comprises or incorporates a digital multimeter.

12 A universal test box as hereinbefore described with reference to Figures 1 to 14 of the accompanying drawings.