MEASURING BRIDGE ARRANGEMENT WITH IMPROVED ERROR DETECTION

Abstract

Disclosed is a measuring bridge arrangement containing: a measuring bridge comprising at least one first half bridge having a first measuring connection and a second half bridge having a second measuring connection; a reference voltage divider having at least one first and a second test connection; a differential amplifier having at least one first and a second amplifier input and at least one amplifier output, a voltage amplification, and having an output voltage working range. In the arrangement, the first amplifier input is wired to a first capacitor and the second amplifier input is wired to a second capacitor, and the amplifier inputs can be selectively connected to the measuring connections or to the test connections.

Claims

1. A measuring bridge arrangement comprising: a measuring bridge with at least one first half bridge with at least one first measuring terminal, and a second half bridge with a second measuring terminal; a reference voltage divider with at least one first and one second test terminal; and a differential amplifier with at least one first and one second amplifier input and at least one amplifier output and with a voltage amplification value (G) and an output voltage working range; wherein the first amplifier input is connected to a first capacitor and the second amplifier input is connected to a second capacitor and the amplifier input is selectively connectable with the measuring terminals or the test terminals.

2. A measuring bridge arrangement as in claim 1, wherein, in a measuring phase, a first switch connects the first measuring terminal, and in a test phase, connects the first test terminal, to the first amplification input, and in the measuring phase, a second switch connects the second measuring terminal, and in the test phase, connects the second test terminal, to the second magnification input.

3. A measuring bridge arrangement as in claim 2, wherein the measuring bridge and the reference voltage divider are operated with a reference potential with respect to a ground, and where the value of a maximum measuring differential voltage between the first measuring terminal and the second measuring terminal multiplied by the voltage amplification value and the value of a reference differential voltage between the first test terminal and the second test terminal multiplied by the voltage amplification value takes values within the starting voltage operating range of the differential amplifier.

4. A measuring bridge arrangement as in claim 3, wherein the voltage value of a common mode signal of the two half bridges is greater by at least half the amount of the maximum measuring differential voltage than the voltage value at the first test terminal, or is less than the voltage value at the second test terminal by at least half the amount of the maximum measuring differential voltage.

5. A measuring bridge arrangement as in claim 4, wherein first time constant values, which each result from the capacitance of the first and second capacitors and the internal resistance of the first and second amplifier inputs, are considerably greater than second time constant values, which each result from the capacitance of the first and second capacitors and the internal resistance of the first and second half bridges.

6. A measuring bridge arrangement as in claim 5, wherein a controller sets the measuring phase and test phase of the first and second switches via a control signal, and in doing so can evaluate a relevant voltage value at the amplifier output.

7. A measuring bridge arrangement as in claim 6, wherein the controller implements a computer program providing the control and performing the evaluation.

8. A measuring bridge arrangement as in claim 6, wherein the controller implements a computer program providing the control signal and performing the evaluation of the relevant voltage value at the amplifier output, to diagnose a first signal processing error state, in particular of the differential amplifier and the analog-digital converter, as well as the integrity of the connections of these elements.

9. A measuring bridge arrangement as in claim 6, wherein the controller implements a computer program providing the control signal and performing the evaluation of the relevant voltage value at the amplifier output, to diagnose a second error state, in particular one caused by a misadjusted or defective measuring bridge.

10. A measuring bridge arrangement as in claim 6, wherein the controller implements a computer program providing the control signal and performing the evaluation of the relevant voltage value at the amplifier output, to diagnose a third error state when one of two signal lines from the least one first half bridge with at least one first measuring terminal, and the second half bridge with a second measuring terminal to the differential amplifier is broken.

11. A measuring bridge arrangement as in claim 6, wherein the controller implements a computer program providing the control signal and performing the evaluation of the relevant voltage value at the amplifier output, to diagnose a fourth error state when both of the two signal lines are broken.

12. A method for error detection in a measuring bridge arrangement as in claim 2, comprising the following steps: application of a reference potential to the measuring bridge and the reference voltage divider; providing a first target range for plausible values of the differential voltage between the first test terminal and the second test terminal multiplied by the voltage amplification (G); setting a test phase by means of the switches; and detection of an error state if the voltage value at the amplifier output is outside of the first target range.

13. A method for error detection as in claim 12, further comprising the following steps: providing a second target range for plausible values of the differential voltage between the first measuring terminal and the second measuring terminal multiplied by the voltage amplification (G); setting a measuring phase by means of the switches; waiting a time that amounts to a multiple of a second time constant, which results in each case from the capacitance of the first and second capacitors and the internal resistance of the first and second half bridges, but a multiple that is smaller than that of first time constants, which result in each from the capacitance of the first and second capacitors and the internal resistance of the first and second amplifier inputs; and detection of an error state when the voltage value at the amplifier output lies outside the second target range or within the first target range.

14. A method for error detection as in claim 12, further comprising the following steps: storage of the error state or states and error circumstances for purposes of additional processing and/or triggering of an alarm and/or signaling a change of operating state.

15. A method for error detection as in claim 13, further comprising the following steps: storage of the error state or states and error circumstances for purposes of additional processing and/or triggering of an alarm and/or signaling a change of operating state.

16. A method as in claim 12, wherein the method is encoded in a computer program, which is implemented by a controller.

17. A method as in claim 12, wherein the method is implemented in a device for parenteral administration of a medication.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 schematically shows an embodiment of the measuring bridge arrangement according to the invention.

[0024] FIG. 2 schematically shows a preferred embodiment of the signal evaluation for a measuring bridge.

DETAILED DESCRIPTION

[0025] In correspondence with a first embodiment of the invention, FIG. 1 shows a measuring bridge arrangement 100 containing a measuring bridge 101, a reference voltage source Vref with reference voltage divider 102, a multiplexer 103 containing two controllable switches S1 and S2, a differential amplifier 104, whose inputs Vin+ and Vin− at the capacitors C1 and C2 are connected with respect to ground and which has an output Vout, a controller 105 containing an integrated analog-digital converter ADC, and a digital control output Stg.

[0026] The measuring bridge 101 is supplied with power by the reference potential Vref with respect to a ground Gnd. Two resistive elements R3 and R4 form a first half bridge having a measuring terminal +UD, where R4 has a fixed resistance value and R3 changes its resistance on the basis of a variable external physical quantity. Two additional resistive elements R1 and R2 form a second half bridge with a measuring terminal −UD, where R1 has a fixed resistance value and R2 changes its resistance on the basis of a variable external physical quantity. Preferably, the bridge is adjusted so that the bridge differential voltage Ua comes close to a zero value at minimal or maximal external values. The common mode voltage Ugt is established at the measuring terminals with respect to ground.

[0027] The reference voltage divider 102 is formed as a series circuit of the three resistors R5, R6, R7 and lies between ground Gnd and reference potential Vref. The test terminal +UR is between R5 and R6 and the test terminal −UR is between R6 and R7. A test voltage Up can be tapped between −UR and +UR.

[0028] The switch S1 in multiplexer 103 is connected by its common terminal COM1 to the noninverting amplifier input Vin+, its normally open contact NO1 is connected to the test terminal +UR, and its normally closed contact NC1 is connected to the measuring terminal +UD. The control line of the switch S1 is connected to an additional output of the controller 105. The switch S2 in multiplexer 103 is connected by its common connection COM2 to the inverting amplifier input Vin−, its normally open contact NO2 is connected to the test terminal −UR, and its normally closed contact NC2 is connected to the measuring terminal −UD. The control line of the switch S2 is connected to a digital output Stg of the controller 105.

[0029] The differential amplifier 104, preferably an integrated circuit of the instrument amplifier type, with the noninverting amplifier input Vin+ and the inverting amplifier input Vin−, has a voltage amplification G (gain), which can be determined by an external element, and an output Vout, which gives the difference of the potentials at the amplifier inputs multiplied by G, provided said value can be represented as a potential between ground and the amplifier supply voltage. The potential at Vout is sent to the analogous input of the analog-digital converter ADC in controller 105.

[0030] The controller 105 can be a hard-wired logic circuit, but preferably is a microcontroller or ASIC that implements a program-controlled logic system using conventional processing and storage components. The controller 105 in the embodiment that is shown controls the multiplexer 103 via the at least one digital output Stg and initiates the analog-digital conversion and the evaluation and processing of the changed measurement value.

[0031] In correspondence with a second, preferred embodiment of the invention, FIG. 2 shows a detachable terminal J200 for the measuring bridge (not shown here; see FIG. 1), a reference voltage supply SUPPLY_REF with reference voltage divider consisting of the resistors R132, R133, R134, a multiplexer N203 containing two controllable switches, a differential amplifier N200, whose inputs Vin+ and Vin− are connected to the capacitors C223 and C222 with respect to ground and which has an output Vo, and a controller U101 containing an integrated analog-digital converter.

[0032] The function and structure of the second embodiment correspond in principle to the first embodiment. The concrete dimensions given below are intended to illustrate aspects of the invention and represent only one possible embodiment. The measuring bridge (not pictured in FIG. 2; see FIG. 1) is connected to the connector J200. The analog multiplexer N203 has two integrated, two-pole, low-resistance switches with low cross talk. The line OCC_SIGNAL_TEST leads the control signal of the master processor U101 to the control input of the analog multiplexer N203. If OCC_SIGNAL_TEST=Low, the inputs NC are connected to the outputs COM, and the inputs NO are open. If OCC_SIGNAL_TEST=High, the inputs NO are connected to the outputs COM, and the inputs NC are open.

[0033] R131 to R134 form a voltage divider circuit at the reference potential SUPPLY_REF, for example 3.0 V. A differential voltage of 22.3 mV with a common mode level of 1.425 V is generated at R133. The two potentials of R133 are sent to the NO1 and NO2 terminals of the analog multiplexer N203. If OCC_SIGNAL_TEST=High, the test signal generated with the voltage divider circuit is present at the two inputs of the amplifier N200. At the set amplification with a Gain=123, N200 generates a reference signal of about 2.75 V. If OCC_SIGNAL_TEST=Low, the two output signals of the measuring bridge are present at the inputs of the amplifier N200. In this mode, the circuit corresponds to the otherwise normal basic circuit for evaluation of the measuring bridge output signals.

[0034] The two capacitors C222 and C223 serve for error detection in the case of a breakage of one or more of the connecting lines to the measuring bridge. The mode of operation is as follows: First, the test signal is evaluated. Through this, the two capacitors obtain a defined potential in the region of the common mode level of about 1.425 V.

[0035] When the multiplexer is switched, the two capacitors, if the connection is intact, take, in a very short time, the potential of the low-resistance measuring bridge as measuring differential voltage with a common mode level of about 1.5 V. The amplified measuring differential voltage is present at the output of N200. On the other hand, if a signal line is broken, the potential of the affected capacitor remains at the original level. For this reason, a comparably high differential voltage of about 75 mV is initiated at the amplifier input, which takes the instrument amplifier N200, with Gain=123, “into account” with (or approach ground GND 0 V or reference voltage SUPPLY_REF 3 V).

[0036] If there is a breakage of both measuring bridge signal lines, the test signal at the output of N200 remains the same. Compared to the normal measuring values, this has an unacceptably high value.

[0037] The output voltage OCC_SIGNAL of the differential amplifier is sent to the analog-digital converter in controller U101 via an analogous low-pass R124, C134. Alternatively, or in addition, the output voltage OCC_SIGNAL can also be sent to a second independent filtering and further processing in additional controller components R230, C344, connecting with controller U200.