DE3013474A1 - SENSOR SYSTEM - Google Patents

Description

Licentia Patent-Verwaltungs-GmbH OK) \ OH IH

Theodor-Stern-Kai 1, 6000 Frankfurt 70

Heilbronn, March 18, 1980 SE2-HN-Ma-et - HN 80/5

Sensor system

The invention relates to a sensor system for determining and transmitting the value of a variable measured variable. It sensor systems are already known in which the measured variables converted digitally and transmitted in the form encoded in this way to an evaluation unit via measuring lines. This can be done, for example, with the help of 4 lines that connect the computer to the sensor. These are a ground line, a power supply line, a data transmission line and a Control line. These lines can be arranged in a star or ring structure. It is also a bus transmission system has already been proposed in which the sensor is in the form of an 8-bit parallel bus system with a microprocessor connected is. * ·.

The invention is based on the object of a sensor transmission system specify where the measured variable can be evaluated reliably and without interference with extremely few transmission lines can be transferred to the evaluation unit. In this system, the data lines are supposed to provide power at the same time of the sensor. This object is achieved according to the invention in that means are provided by which the measured variable in the form of a pulse over the sensor lines which are also the power supply lines of the Sensors are, transmitted HqaMl · »- ^^ gHw being, where the pulse width is a measure of the measurand.

130042/0198

"Ir-" '3013A74

In this sensor system, an evaluation unit is provided to determine the pulse width, which is connected via a double line is connected to at least one controllable sensor via the line. This evaluation system is for example a data processing system or a microprocessor, via or through the using the double sensor line a current can be fed into the sensor during the query phase.

The sensor system according to the invention thus only requires two lines, via which both the power supply takes place the measured variable is also transferred to the evaluation unit. If several sensors to be queried are connected to the evaluation unit are, these sensors preferably have a common ground line, so that from the evaluation unit to only one cable has to be routed to each sensor. The sensor is only activated during a defined query phase, so that the power expenditure is extremely low. The value of the measurand results exclusively from the Width of a pulse transmitted via the sensor lines, so that the measured variable by counting or scanning this pulse width, for example with the help of a programmable Microprocessor easily identified and converted to an analog value converted or output as digital size.

In the invention, the sensor contains a circuit through which the output impedance of this sensor is preferably in the Query phase is changed by leaps and bounds. The sensor line system is thus used for the evaluation unit during the query phase once recognized as high resistance and after a certain time as low resistance or vice versa. The time that between the start of the query phase and the occurrence of the impedance jump is proportional or vice versa proportional to the measurand and is displayed directly in the

130042/0198

J

Evaluation unit determined. In a further preferred embodiment, the time between the start of the Query phase and the occurrence of the impedance jump inversely proportional to the logarithm of the measured variable. Included the interrogation phase of the sensor is chosen so large in time that every possible pulse width during this interrogation phase is detectable.

Another possibility is to start the query phase; to terminate immediately after the impedance jump is determined by the evaluation unit. ,

The circuit itself therefore preferably contains a time-determining one Element that can be connected to a power source, the output from the power source in the query phase and the current charging or discharging the capacitor is dependent on the respective value of the measured variable. To the time-determining Link is then connected to a switching unit through which the potential is dependent on time Conditions on the time-determining element an impedance ignition circuit between the two input terminals of the sensor in a manner detectable by the microprocessor is triggered. This time-determining element is preferably a capacitor which is connected to the input of the impedance switch causing Schmitt trigger is connected.

With the system according to the invention, for example, on Sensor prevailing temperatures, pressures, flow rates, Light intensities or humidity can be measured. It is essential that the current delivered by the power source, with which a capacitor is charged or discharged, for example, is a function of the measured variable.

The invention and its further advantageous refinement are to be described in the following on the basis of an exemplary embodiment are explained in more detail.

130042/0198

The block diagram of the sensor ./ Transmission system shown.

FIG. 2 shows the pulses transmitted via the line system and representing a measure for the measured variable. In FIG. 3 shows the sensor circuit which contains a Schmitt trigger and a current source. Fig. 4 shows an embodiment for the Schmitt trigger circuit. In Fig. 5 is an embodiment for the power source shown when this should deliver a current that is dependent on the temperature at the sensor. Fig. 6 shows a part!, Circuit from which another Possibility for the discharge of the time-determining member after the end of the query phase results.

1 shows a sensor 1 which is connected to the evaluation unit M and the current source Q via a double line 2. The input terminals of the sensor are numbered 2a and 2b. The evaluation unit M is preferably a programmable microprocessor which also includes the current source Q ₁ . This current source is activated according to the specified program of the processor and feeds an impressed current i in the query phase ^. for example of 1 mA, at a maximum voltage of 5 V in the sensor line 2. The voltage and current conditions at the input terminals 2a, 2b of the sensor during the query phase are shown in FIG. 2. '

The query phase includes the period t, which is chosen as large is that every pulse width generated in the sensor can be detected by this time t. The sensor is too

next low-eared, so that the voltage at the beginning of the query phase from the fourth O to the value Al of, for example, 1 mA. R. jumps, where R. is the state-dependent resistance of the sensor at input terminals 2a and 2b.

T30042 / CH9 *

This voltage A1 is shown in FIG. 2 and has "for example a value of 1 V. A1. must in any case be significantly below the maximum voltage of 5 V, for example, due to the appropriate dimensioning of the sensor circuit. The evaluation unit M connected to the sensor 1 thus recognizes the sensor status as low-resistance. After a certain time t. the sensor switches to a high-resistance state. This reduces the current i. from the value i to a very small value i ". i »is, for example, 10 μΑ. At the same time, the voltage between the sensor terminals 2a and 2b jumps from the value μ to the value μ _ο , which is specified by the microprocessor. μ is, for example, 5V ". The microprocessor now recognizes the sensor as high resistance and is able to count the time t. is a measure for the measured variable determined by the sensor, for example for the temperature prevailing at the sensor.

After the time t, the query phase ends and the sensor will

P * ■

switched off by the microprocessor, which means that both the Both the voltage and the current at the sensor input go back to O. In another case, the microprocessor will do so programmed that the query phase is terminated by him after the impedance jump has been registered, so that the microprocessor additional working time for other tasks is gained.

In Fig. 3, the circuit contained in the sensor is shown. If it is implemented using integrated semiconductor technology, this circuit has three output pins P ₁ , P "and P_. Between the pins P2 and P ₃ , the capacitance C ^ , which can be connected externally if necessary, is used to determine the time.

130042/0198

/ tO

Mende member forms, switched. This capacity is preferably integrated, e.g. B. in the form of a MOS capacitance. In this case, pin 2 is omitted. The sensor transmission lines end at pin P or P, respectively. The Schmitt trigger with its power supply electrodes F and G is located between the pins P and P _3. The current source Q ″ is connected to the input of the Schmitt trigger ST ″, which charges the downstream capacitor C- with a current dependent on the measured variable _{A resistor R 9 is} connected to the output A of the Schmitt trigger ST, which determines the low-resistance state of the circuit and which only carries the current i, - during the charging phase of the capacitor CU, ... during the query phase of the Schmitt trigger, a switch T is driven, the current source Q ₉ only to the capacitor C ^ via the - is connected during the charging Further, the circuit includes means by which when turning on the current source Q ₉ to the capacitor C- ^ this. is charged to a defined bias voltage, so that the actual charging phase of the capacitor C ^ always begins with a defined basic setting Otherwise by 2 or more diodes, D ^, which are connected to the switch T via a series resistor R ^. The switch T is, for example, a transistor whose base-emitter path is parallel to a resistor R ₁ , which is connected in series with the resistor R ₉ between the output A of the Schmitt trigger and pin P ...

As soon as a current is impressed via the sensor le.itungeη at the beginning of the query phase t, the Schmitt trigger ST is switched on in such a way that the output electrode A has a low or ground potential. In this case, _{current can flow through the resistor R 9} , as a result of which a sufficient voltage, which controls the transistor T, drops across the resistor R. The resistor R ₉ has a relatively low resistance, for example 100-400 Ω and essentially determines the current i ^ according to FIG. 2. As soon as the transistor T is switched on

130042 / 01Θ8

/ M-

is, the capacitor C _r is charged via the resistor R_ and the diode D_ to the voltage _{value specified by the diode D 3.} The diodes D, are parallel to the series circuit of diode D ₂ and capacitor C ^; , the resistor R ^ is chosen so that the capacitor Cy * through the diodes D-. assumes a given voltage very quickly. This ensures that the capacitor Cj- is always charged from a defined basic charge at the beginning of the query phase. Further charging takes place via the current delivered _{by the current source Q 7.} This current is, for example, a function of the temperature prevailing in the vicinity of the current source Q ". The current i, with which “the capacitor Cf is charged further, is, for example, at a temperature T, 10 μΑ and changes with every degree of temperature change by approx. 1 %.

When the capacitor C ^ is charged to a voltage predetermined by the threshold voltage of the Schmitt trigger ST, this voltage present at the input E of the Schmitt trigger triggers the switching of the Schmitt trigger, whereby a current flow through the resistor R " at the output of Schmitt trigger A becomes impossible. As a result, the transistor T- is also blocked and the current source Q ~ is switched off. The capacitor Gj * can therefore no longer be charged. This switchover takes place after time t (FIG. 2). This switches off both the current I ₅ and the current I ₃ and the current i. Only the current i. Required to supply power to the Schmitt trigger flows via P .., which is 10 μΑ, for example, and thus determines the high-resistance state of the sensor.

The capacitor C ^ is connected to the sensor line via a diode D- at pin P, connected in such a way that after the query phase t by briefly grounding this sensor line a discharge of the capacitor up to the caused by the di-

130042/019 8

de D, certain flux voltage is possible. The grounding of the sensor line is after time t cessor triggered by the micro- * short term. This ensures that when the sensor is interrogated again, the discharged state of the capacitor Cj- can be assumed.

In the case of the current source Q, it is assumed that the their output current is a function of temperature. However, this current can also function as a pressure which Brightness, the humidity of a speed or flow rate.

The configuration "of a Schmitt trigger results, for example, from FIG. 4. The circuit consists of the npn transistors T-, T".; the pnp transistor T "and the downstream transistor T_, through which the resistor R_ is connected to ground When the capacitor C ^ is discharged, no current can flow through the transistor T., whose base is connected to the capacitance Ο.γ. This increases the collector potential of the transistor T. so that the transistor T_. is switched through via the base resistor R _g . A current now flows through the collector resistor R i. of the transistor T-, and via the emitter-

resistance R ₀ , which is also the emitter resistance of the transit

stors T. is. As a result, the transistor T _{2 coupled to the resistor R 1} on the base side is also switched through, so that current flows _{from the resistors R., R 5} via the voltage divider located in the collector branch of the transistor T_. The voltage drop across the resistor R supplies the base-emitter voltage of the transistor T ₇ , which is switched through when the resistor is dimensioned accordingly. so that the resistor R _{2 is} connected to ground via the collector-emitter path of the transistor T _7. In series with the resistor R ₂ is the base-emitter path of the transistor T-bridging resistor R ₁ , across which a sufficiently large voltage drops to durehzusteuern the transistor T., so that now the current-

130042/0198

source Q "is connected to pin 1 and thus the capacitor Cj- via the current source Q _? can be charged.

In the case of a charging voltage on the capacitor C > £ * and thus on the input E of the Schmitt trigger resulting from the resistance ratio of R _{g and R i, the transistor T 4 is switched} through, whereby the transistors T _{1 and T 2 are} blocked. This also blocks the transistor T ₇ and a current flow through the resistor R "becomes impossible. The transistor T. Now only current can flow through the collector-emitter section of the transistor T. Due to the corresponding high-resistance dimensioning of the resistors R_ and R ₀ , this current is of the order of magnitude

/ 8th

for example 10 μΑ. With the transistor switched on In contrast, a significantly larger current sometimes flows, which is determined in particular by the low-resistance R " will.

Finally, FIG. 5 shows an exemplary embodiment for the current source Q _? that deliver a temperature-dependent current i *. The circuit consists of the two npn transistors T- and Tg, the base-emitter path of the transistor T _{5 being} parallel to the collector-base path of the transistor T _c . the

Base-collector path of the transistor T _c is with the

high resistance R ₁₁ bridged, while parallel to the base-emitter path of the Tr
ohmic resistance R ₁ - is.

to the base-emitter path of the transistor T _c a low-

_{When the current source Q ″ is connected to P 1} via the output poles D and C and the transistor T, which is switched through, a voltage _{which opens the transistor T 5 initially drops across the resistor R.} The current flowing through the transistor T ₅ rises until the voltage across the resistor R-

130042/0198

-Ak-

U, which is required to control the transistor T _fi ., Drops. If U is approximately equal to 0.6 V and the resistance R _{1 is} “60 kn , then this is the case with a current of 10 μΑ. When T, - becomes conductive, the transistor becomes

T _{c of} the base current withdrawn, so that the current i in wesentb -οι _m

borrowed by the resistance R ₁ "is determined. The voltage U _R _ has, for example, a negative temperature coefficient of −0.4 % / K, while the resistor R "has a positive temperature coefficient of, for example, 0.5 % / K

BE

having. Since the current essentially passes through i =

m R

is determined, there is a current decrease of approx. 0.9 % / K for every degree of temperature increase. The components can be chosen so that with one degree increase in temperature, the current decrease is - ^ 1 % .

The absolute current at a defined temperature value can vary from source circuit to source circuit with the component tolerances vary. In this case it will make sense to use the capacitance C ^. the absolute value of the current of each to adapt the power source used. This can also be done with the help of an automatic capacity adjustment.

The circuit of FIG. 5 shows that the current becomes smaller and smaller at very high temperatures, so that the capacitance C γ is charged more slowly. As the temperature increases, the pulse width t .. according to FIG. 2 increases.

Another circuit possibility results from FIG. 6 in order to safely discharge the capacitor C? "After the end of the query phase, in which case no additional grounding of the sensor line arriving _{at pin P 1 is required} 3. The circuit parts which are not shown correspond to those of FIG. 3, the diode D being omitted.

1300A2 / 0198

_. / 15.

According to FIG. 6, the source _rf drain path of a MOS field effect transistor T ₀ is connected in parallel to the capacitor C γ by the

arming type switched. The gate electrode of this transistor Τ «is connected to the sensor line 2a _{via a suitable series resistor R 1.} Furthermore, a protective circuit for overvoltage peaks is arranged between the gate electrode and the ground line 2b. This circuit consists, for example, of a series of diodes D- connected in series, for the control of which a voltage of more than 5 volts is required.

At the beginning of the query phase, practically the entire voltage XX is applied to the gate electrode. (Fig. 2), which with appropriate selection of the. MOS field effect transistor T-. of the impoverishment type is sufficient to constrict its channel. The capacitor C «can therefore be charged _{via the current source Q 5.} The circuit from the series resistor R

Z the sensor circuit was de-energized because the voltage

and the diode path D _{0 also} remains in the high-resistance supply

is not sufficient to control the diode path D _ß .

After the query phase has ended, the gate potential at transistor Τ goes. _φ back to the? value 0 and the transistor assumes its normally-on state, so that the capacitance Gj. can discharge through the MOS transistor.

The circuit according to the invention or the sensor system has the advantage that a quasi-digital transmission of the measured variable is possible without critical current or voltage levels and a simple evaluation routine can be carried out in a microprocessor.

130042/0198

Claims (19)

Licentla "Patent-T-Vexwal ^ tuTTjiS-G. M.b. H. Theodor-Stern-Kai 1, 6000 Frankfurt 70 301 3 A 7 Heilbronn, 18.O3.8O SE2-HN-Ma-et - HN 8O / 5 Claims I) J sensor system for determining and transmitting the value of a variable measured variable, characterized in that means are provided through which the measured variable is transmitted in the form of a pulse via the sensor lines (2) which are also the power supply lines of the sensor, with the pulse width is a measure of the measurand. 2) Sensor system according to claim 1, characterized in that an evaluation unit (M) is used to determine the pulse width is provided and that this evaluation unit has a double line (2) or a single line with ground line, is connected to at least one controllable sensor (1) via the line. ·. 3) Sensor system according to claim 1 or 2, characterized in that that the evaluation system (M) is a data processing system or a microprocessor and that this evaluation unit is a current (i.) via the sensor line (s) (2) can be fed into the sensor (1) during the query phase of the sensor. 4) sensor system according to one of the preceding claims, characterized in that the sensor (1) is provided with a circuit (Fig. 3) through which the input impedance of the sensor changed abruptly in the query phase (t) 130042/0198 where the time (t.) between the start of the query ./ phase and the occurrence of the impedance jump is proportional
to the measurand. 5) Sensor system according to one of claims 1-3, characterized in that the sensor (1) is provided with a circuit (Fig. 3) through which the input impedance of the sensor in the query phase (t) is changed abruptly, the
Time (t,) between the beginning of the query phase and the occurrence of the impedance jump is inversely proportional to the measured variable. - 6) Sensor system according to claim 5, characterized in that the time (t ..) between the start of the query phase (t) and the occurrence of the impedance jump is inversely proportional to the logarithm of the measured variable. 7) sensor system according to one of the preceding claims,
characterized in that the query phase (t) des
Sensor (1) is chosen so large in time that every possible pulse width (t,) can be detected during this query phase (t). 8) Sensor system according to one of the preceding claims, characterized in that the query phase (t) of the sensor (1) is terminated after the impedance jump has been determined by the evaluation unit (M). 9) sensor sy star according to a d ^ £ L_y_orangehen claims,
gekjeimzeich thereby that the circuit (Fig. 3) of the
Sensor contains a time-determining "element (CL.), The
to a Stromquell§_4 ^ yt ^ can be switched on, the of
current delivered by the power source in the query phase (i)
depends on the respective value of the measurand. 130042/0198 10) A sensor system according to claim 9, characterized in that a Umschaltein- ■ standardized to the time-determining member (Cj) * (ST) is connected, the impedance change in timed relation to the potential conditions at zeitbes'timmenden member (Q ^) dureh between the two input terminals (2a, 2b) of the sensor is triggered. 11) Sensor system according to claim Xj or VO, characterized in that the current delivered by the current source (Q ₂₎ (i) the temperature prevailing at the sensor, m a pressure, a flow rate, a light intensity or a moisture dependent. 12) sensor system according to one of the preceding claims, characterized in that the tent-defining member is a Capacitor (C ^) is connected to the input of a Schmitt trigger (ST) is connected. 13) Sensor system according to claim 12, characterized in that at the output (A) of the gchmitt trigger (ST.) A resistor (R ₂ ) which determines the low-ohmic state of the circuit is connected, which is only in the charging phase of the capacitor (C ^ ) while Seir query phase (t _p ) carries current (ig), 14) Sensor system according to claim 12 or 13, characterized in that a switch (Τ _χ ) is controlled via the output (A) of the Schmitt trigger (ST) Wi * <ä, via which the current source (Q ₂ ) is connected to the capacitor ( C ^) is connected during the charging phase « 15) Sensor system according to claim 14, characterized in that means (R ₃ , D ₃ ) are provided through which, when the power source (Q) is switched on, the capacitor (Cy) is charged to a defined bias voltage. 130042/0193 16) Sensor system according to claim 15, characterized in that that two or more diodes (D-) are connected in parallel to the capacitor (Cv), which are connected via a series resistor (R3) connected to the switch (T.). 17) sensor system according to one of the preceding claims, characterized in that the capacitor (C ^) over a diode (D,) is connected to the sensor line in such a way that after the interrogation phase (t) by brief earthing of this sensor line, the capacitor can be discharged except for the forward voltage determined by the diode (D.). 18) Sensor system according to one of claims 1-16, characterized in that the capacitor _{is bridged by the source-drain path of a MOS field effect transistor (T Q} ) of the depletion type, the gate electrode of which is connected to the supply line (2a), so that at the beginning of the query phase the MOS field effect transistor (Tg) is blocked. 19) The sensor system according ^v of the preceding claims, characterized in that the current source (Q_) for generating a temperature-dependent charging current (i) for the capacitor (Cj) consisting of two transistors (Tj, T _g) is the same zone sequence, wherein the Base-emitter path of the first transistor (T ₅ ) is connected in parallel to the collector-base path of the second transistor (T _g ), while parallel to the base-collector path of the first transistor (T ₅ ) and parallel to the base-emitter path of the second transistor (Tg) a resistor (R-, η or R ,,) is connected, so that the temperature response of the base-emitter voltage of the second transistor (T_) together with the temperature response of the resistor (R ..) connected to this voltage, the temperature dependence of the through determine the source of current flowing (i). 130042/019 *