GB2438024A

GB2438024A - Valve Controller

Info

Publication number: GB2438024A
Application number: GB0609314A
Authority: GB
Inventors: Mark Christopher Turpin; Janet Marie Turpin
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-05-11
Filing date: 2006-05-11
Publication date: 2007-11-14
Also published as: GB0609314D0

Abstract

A valve controller, for the operation of a latching solenoid valve, which is closely coupled to the valve and may be built into the solenoid. The controller stores energy sufficient to set the valve to a safe condition in the event of a power or control system failure. The controller additionally allows the valve to be controlled by a digital logic signal, which can be unmodulated, or for greater security can be modulated by a central controller, to ensure that the valve returns to a safe condition in the event that the central controller fails. The valve controller can be adapted for individual addressing of valves along a digital bus.

Description

Valve Controller

Background

A magnetically latching solenoid valve has been described in various documents and is detailed in US patent 4,383,234. The brief principle of operation is that the valve is opened by a current pulse through the solenoid valve coil. The magnetic flux generated in the coil lifts the valve armature, which is then magnetically coupled to a fixed magnet and thereby prevented from re-seating, even though the coil current is removed. At some later time the valve is closed by a reverse polarity current pulse in the solenoid valve. This closing pulse acts to pull the armature free of the fixed magnet and re-seat the valve to effect closure.

These so-called latching solenoid valves have found wide and varied use in applications where power is limited, particularly in battery operated applications. A good example of such applications, is in garden watering or sprinkler systems, wherein it is desirable to have remote actuated valves, but undesirable to have to wire power to each valve. For these applications a magnetically latching solenoid is usually the solution of choice.

An application where the current solution is less satisfactory is in the control of flammable gases for domestic appliances, or indeed for any valve wherein the medium is hazardous. The use of a battery operated solenoid is desirable, allowing the user to control the appliance from an electronic control panel. However, the outcome in the event that the battery should fall whilst the valve is actuated, leads to a safety issue. In this situation, the valve controller will be unable to close the valve until a new battery is installed. It is therefore necessary, in this situation, to have an auxiliary manual valve, or some form of manual override on the solenoid valve. The use of an auxiliary valve is the solution most often adopted, thereby forcing the appliance to be supplied via two valves at considerable additional cost.

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Description of the Invention

The invention of this disclosure comprises a small electronic controller which, when fitted to a magnetically latching solenoid valve, causes the valve to operate as a non-latching valve, whilst maintaining the low power properties of the latching valve.

The circuit consists of a microcontroller with inputs/outputs including 1. Two analogue inputs capable of indicating voltages up to the level of the valve operating voltage. The input may be an analogue to digital converter able to report absolute voltages to the controller, or may more simply comprise a comparator, which compares the voltage input with a known reference.

2. A digital input to the controller which is externally switched between logic states to indicate whether the valve should be open or closed.

3. Three logic outputs whereby a high voltage is deemed to be logic state 1' and a low voltage is deemed to be logic state'O'.

External to the microcontroller is a circuit whose function it is to translate the logic outputs from the microcontroller into a current pulse, suitable to either open or close a magnetically latching solenoid valve. Also external to the microcontroller, is a charge storage device, comprising a capacitor, an electrochemical charge storage device or a superconducting charge storage device. In each case the charge storage device must hold sufficient charge to be capable of delivering a current pulse sufficient to operate the valve. The charge storage device may be a single component operating at the voltage required by the valve, or may store energy at a different voltage to the valve requirement and actuate via an interconnection circuit. This latter approach is valuable when the charge storage device is a so-called ultracapacitor that is limited in operating voltage to 2.3 V. In addition to the primary charge store, a secondary charge storage device is desirable. This unit stores power to allow the microcontroller to operate, for sufficient time to effect a valve operation, after power is removed from the circuit. It is feasible to draw this power from the primary charge storage device provided the microcontroller is protected from the effects of the rapid decline in input voltage when the valve is actuated. A block schematic of the system is included in Figure 1. The operation of the device is as follows.

When power is applied to the circuit, the microcontroller takes control of the valve controller and sets logic outputs consistent with placing the valve in a safe condition. The microcontroller also monitors the voltage across the charge storage device, which begins to charge as soon as power is applied to the circuit and is prevented from discharging by the gate. Once the microcontroller has determined that the charge storage device is charged to a suffIcient potential to operate the valve, the controller polls the external logic circuit and instructs the valve controller to operate the valve accordingly. During this operation the gate remains closed and power for the valve is drawn from the external power supply. The microcontroller now cyclically polls the external logic and the power supply voltage. In the event of an external logic change, the controller simply operates the valve in accordance with the new instruction. In the event that the power supply voltage drops below some defined limit the microcontroller begins a shutdown sequence. To effect the shutdown sequence the controller opens the gate that controls the output from the charge storage device and then instructs the valve to return to the user defined safe condition. Power to operate the valve is drawn from the charge storage device; thereby the shut down sequence is operable in the complete absence of external power, or indeed in the event that the external system has been destroyed.

The operation of the valve controller is shown in the form of a flow diagram in Figure 2.

A specific preferred embodiment of the invention will now be described by reference to these drawings and to the circuit diagram included in Figure 3. The preferred embodiment is intended for illustration and is not intended to restrict the claims to any particular design.

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Preferred embodiment In the circuit shown in figure 3 positive and ground power rails enters the circuit through conni. The positive rail is split by two diodes, D2 and D3, to power the microcontroller and the valve circuit respectively. The voltage in the microcontroller power circuit is moderated to 5V by a 78L05 voltage regulator, U2, and a further diode, Dl, which prevents charge leakage from the microcontroller when the power line fails. Local to the microcontroller, a capacitor C2, stores enough charge to allow the controller to operate for approximately l500ms after the power has failed. The incoming power line voltage is monitored by the microcontroller at the voltage divider R9/Rl0.

Within the valve control circuit the charge storage device is a capacitor, Cl. This capacitor is sized to deliver a suitable current pulse to operate the valve solenoid Soll. The majority of small valve solenoids operate at a power of 6W regardless of operating voltage. In addition, a valve will typically require a current pulse of 75ms duration to operate reliably. Knowing this information, we can estimate the required capacitance to be of the order of 1000-20,000uF depending on the valve voltage. For a 6 volt valve the use of a 10,000uF capacitor has been found experimentally to be appropriate. This implies that for a 12 volt valve a 3300uF capacitor will be adequate, whilst at 24V a l000uF capacitor will suffice. Critical to the ability of a given capacitor to operate the valve is the equivalent series resistance (ESR); this parameter gives a measure of the resistance to current flow from the capacitor during discharge. The ESR of the capacitor used in this example was approximately 1 ohm.

The charge storage device is charged via a diode D4 which prevents discharge of the stored charge. In order to discharge Cl the gate, in the form of a silicon controlled rectifier (SCR), Q7, must be opened by the microcontroller. The voltage across the charge storage device is measured via a resistive divider R4/R6 and is monitored by the microcontroller.

The remainder of the valve control circuit is generally referred to as an H-circuit or H-bridge.

The circuit reverses the polarity applied to the solenoid, soil, dependent on whether a small current is applied to the base of Qi or Q3. The required current is supplied from the microcontroller logic output.

The microcontroller used in this example is a Microchip PlC 12F629 which has the following pin-out configuration in this application

Pin Description Application

1 Power Vss 2 Logic output O/5V Open Valve 3 Logic output O/5V Close Valve 4 Logic Input/0/5V External logic control with pull-up via R8 Logic Output O/5V Gate Control 6 Analogue Input O-5V Charge storage device voltage 7 Analogue Input 0-5V Incoming power line voltage 8 Ground Vdd Operation of the preferred embodiment 1 The following relates specifically to the operation of the circuit in Figure 3 when used to drive a 6 volt solenoid. It is intended to illustrate one mode of operation of the valve controller rather than to limit the utility to a particular set of conditions.

On the application of power the microcontroller starts and sets internal operating parameters and operates the valve into a safe condition (closed) by pulsing pin 3 high for 1 OOms. The microcontroller monitors the voltage at Cl until this exceeds 4.9V. Once Cl is charged the controller reads pin 4 and, if this is high, will open the valve via a lOOms pulse to logic high

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at pin 2. The controller now monitors the voltage on the incoming power line at pin 7 and ensures that this remains above 5V. The controller also monitors the external logic line via pin 4 and sets the valve in accordance with requirement via pins 2 and 3.

In the event that the line voltage falls below 5V, the microcontroller opens the gate by setting pin 5 to logic high and then closes the valve with a lOOms logic high pulse to pin 3, followed by a logic low signal to pin 5. Once the valve has been closed, the controller returns to monitor the power line and will return the valve condition to that set via the external logic input in the event that the power is restored and the charge storage device is recharged. After approximately l500ms the charge in C2 declines to a point where the microcontroller shuts down. The PlC 12F629 has a brown-out detection circuit which ensures that the chip shuts down in an orderly manner when the input voltage maintained by C2 falls below 2 volts.

The circuit described in the preferred embodiment is compact enough to be installed within the body of the solenoid and this is an ideal arrangement to ensure safety. However, the high magnetic flux within this area means that screening of the circuit from spurious induced signals is quite difficult and requires some skill and experimentation to devise a satisfactory arrangement.

Operation of the preferred embodiment 2 The following relates specifically to the operation of the circuit in Figure 3 when used to drive a 6 volt solenoid. It is intended to illustrate one mode of operation of the valve controller rather than to limit the utility to a particular set of conditions.

This operation of the preferred embodiment is identical to the preceding, with the exception of the operation of the external logic signal at pin 4.

For additional security of operation the external logic signal can be adapted to receive a timing pulse that indicates that external circuits are functioning correctly. In this mode the microcontroller is programmed to open the valve when a correctly modulated signal is detected at pin 4. For this mode of operation it has been found ideal for the modulated signal to be a square wave with a full cycle frequency of between 1 and 1000 Hz. The microcontroller is programmed to turn on the valve when a modulated signal is detected and to turn off the valve in the event that the modulated signal stops or the power fails.

This arrangement can give an additional level of security to valve operation particularly when the valve controller is itself controlled by a second controller which may crash or hang, and whilst in this condition may maintain an output to the valves logic control line.

Operation of the preferred embodiment 3 The following relates specifically to the operation of the circuit in Figure 3 when used to drive a 6 volt solenoid. It is intended to illustrate one mode of operation of the valve controller rather than to limit the utility to a particular set of conditions.

In many applications it is desirable for numerous valves to be controlled by a central control system and this generally involves running separate wires from the controller to each valve.

This wiring and control arrangement can be avoided by arranging the central controller such that it transmits through a single wire a binary code that instructs a number of connected valves as to which should be open and which closed. The valve receives the code at pin 4 and interprets the code into a single instruction of relevance to that particular valve. By re-transmitting the code on a suitable time cycle, preferably at least once every second, and most preferably once every millisecond, the valve receives continuous updates as to status. The simplest arrangement to achieve this is for the central controller to transmit a binary code, within which each bit codes the status of one valve in the system, with an additional one to four bits that validate the signal via a check-sum.

In the event that the incoming transmission is interrupted or stops or in the event that the valve power supply fails the valve will be actuated to a safe condition by means of the charge stored within the charge storage device.

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Claims

Claims 1. A valve controller suitable for the operation of a latching

valve, whereby the controller stores sufficient electrical power to unlatch the valve in the event that the circuit power should fail.

2. A valve controller as in claim 1 whereby the electrical power is stored in a capacitor.

3. A valve controller as in claim 1 whereby the electrical power is stored in an electrochemical device.

4. A valve controller as in claim 1 whereby the electrical power is stored in a superconducting coil.

5. A valve controller as in claims 1 to 4 wherein the stored electrical power is protected from discharge during normal operation of the valve by an electronic gate circuit that is only opened in the event of a power failure.

6. A valve controller as in claims 1 to 5 wherein the controller is incorporated into the solenoid enclosure.

7. A valve controller as in claims 1 to 5 wherein the controller is mounted in close proximity to the valve.

8. A valve controller as in claims 1 to 7 wherein the controller opens or closes a valve according to the presence or absence of a low voltage control signal on an incoming data line.

9. A valve controller as in claims 1 to 7 wherein the controller opens or closes a valve according to the presence or absence of a modulated control signal on an incoming data line.

10. A valve controller as in claim 9 wherein the modulated signal is encoded with information that identifies an operation and the specific valve to which the instruction applies.

11. A valve controller as in claim 10 wherein the encoded signal comprises a binary part, within which each bit instructs one valve on or off, coupled with a checksum that is used to validate the signal. -10 -