Piezoelectric measuring device and method for operating a measuring device

Abstract

To provide a piezo-electric measuring device.SOLUTION: A piezoelectric measuring device of the invention comprises a sensor element and a conductor element. The sensor element comprises an operational amplifier comprising an inverting input and an output. The sensor element comprises a feedback capacitor arranged in parallel with the inverting input and the output of the operational amplifier, and a reset switching element arranged in parallel with the inverting input and the output of the operational amplifier. A data acquisition device comprises a measurement cycle circuit configured to provide supply voltage to the sensor element, to switch on the supply voltage to the sensor element before starting of a measurement cycle, and to switch off the supply voltage after completion of the measurement cycle. The sensor element comprises a power-on reset logic designed to detect presence of the supply voltage and to close and reopen the reset switching element if the supply voltage is present before the starting of the measurement cycle.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a piezoelectric measuring device for measuring pressure, which is particularly used in the field of injection molding dies for measuring cavity pressure. In particular, the measuring device according to the present invention is characterized by a reliable or safe measurement of the cavity pressure, respectively. Furthermore, the present invention relates to a method of operating a measuring device designed in the manner according to the present invention.

Background Art

[0002] A piezoelectric measuring device including the features of the preamble of claim 1 is known from Swiss Patent Invention No. 542434. The piezoelectric measuring device includes a sensor element. The sensor element includes a piezoelectric element, an operational amplifier, a feedback capacitor, a discharge resistor, and a reset switch. The cavity pressure to be measured acts on the piezoelectric element as a force. Under the influence of the force, the piezoelectric element generates an electric charge. The electric charge is converted into a voltage signal by the operational amplifier. The feedback capacitor is arranged in parallel with the inverting input of the operational amplifier and the output of the operational amplifier and functions as an integrator. The discharge resistor and the reset switch are also arranged in parallel with the inverting input of the operational amplifier and the output of the operational amplifier. The discharge resistor continuously discharges the feedback capacitor so as not to become overloaded after a while due to a fault current in the sensor element, and this fault current occurs in a quasi-static measurement particularly due to only the finite high electrical insulation resistance of the sensor element. Then, by closing the residual switch, the feedback capacitor is discharged before the start of the measurement to cause zeroing of the sensor element. During the measurement, the residual switch is opened.

[0003] Furthermore, in the piezoelectric measuring device disclosed in relation to FIG. 2, it is known from WO 2014 / 120430 that a data acquisition device having a switch is provided. The switch is used to switch different power voltage sources.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Swiss Patent Invention No. 542434 [Patent Document 2] Pamphlet of International Publication No. 2014 / 120430 [Summary of the Invention]

[0005] The piezoelectric measuring device according to the present invention includes a sensor element designed to generate a measurement signal for the measured pressure. The piezoelectric measuring device includes a cable for transmitting the measurement signal to a data acquisition device, and the data acquisition device is designed to acquire and evaluate the transmitted measurement signal. The sensor element includes an operational amplifier having an inverting input and an output. The sensor element includes a feedback capacitor arranged in parallel with the inverting input and the output of the operational amplifier. Further, the sensor element includes a reset switching element arranged in parallel with the inverting input and the output of the operational amplifier. And the data acquisition device is further designed to provide a power supply voltage to the sensor element.

[0006] The piezoelectric measuring device according to the present invention including the features described in claim 1 is based on the idea of constructing a sensor element known from the prior art with an operational amplifier and a feedback capacitor without using a discharge resistor.

[0007] Despite omitting a discharge resistor for discharging the feedback capacitor, the present invention provides reliable discharge of the feedback capacitor with a relatively small circuit and enables quasi-static measurement.

[0008] Accordingly, in light of these explanations, the piezoelectric measurement device according to the invention having the features of claim 1 is designed such that the data acquisition device of the measurement device further comprises a measurement cycle circuit designed to switch on the power supply voltage for the sensor element before the start of the measurement cycle and to switch off the power supply voltage after the completion of the measurement cycle. Accordingly, according to the invention, the sensor element has a power-on reset circuit, and the power-on reset logic is designed to detect the presence of the power supply voltage and to close and then open the reset switching element when the power supply voltage is present before the start of the measurement cycle. Accordingly, the feedback capacitance is at least indirectly discharged before the start of the measurement cycle.

[0009] Advantageous developments of the piezoelectric measurement device are described in the dependent claims.

[0010] In particular, the measurement cycle circuit includes a power supply switching element for turning on or off the power supply source for the sensor element.

[0011] Preferably, the discharge of the feedback capacitance by the power-on reset circuit is carried out by a power-on reset circuit designed to operate the reset switching element to discharge the feedback capacitance.

[0012] Furthermore, it is preferable that the data acquisition device comprises a tare circuit designed to tare the first measurement signal transmitted from the sensor element. In particular, this enhances the measurement accuracy in subsequent stages of the measurement.

[0013] A preferred development of the reset circuit is designed to include a power-on reset logic that closes and then opens the reset switching element to discharge the feedback capacitance after exceeding a predetermined voltage value at a specified time.

[0014] The present invention also enables signal transmission and power supply to the sensor element via a conductor element, which is a single-core cable having a single signal conductor. Thus, no additional conductor is required to trigger the reset with the feedback capacitance, which is particularly advantageous in injection molding dies where limited space is dominant.

[0015] Also, in an alternative circuit, the sensor element 10 may be provided with a 4..20 mA transmitter and a current interface. The 4..20 mA transmitter is connected to the output of the operational amplifier and is designed to convert the measurement signal provided by the operational amplifier as a voltage signal into a current signal. The 4..20 mA transmitter is connected to the current interface. The current interface is connected to the conductor element. The current signal is transmitted from the 4..20 mA transmitter to the data acquisition device via the current interface and the conductor element. Further, the data acquisition device includes a shunt element connected downstream of the voltage supply source and a further operational amplifier. The shunt element and the further operational amplifier are designed to convert the transmitted current signal back into a voltage signal. Thus, the measurement signal is transmitted from the sensor element to the data acquisition device in a current-adaptive manner. This is particularly advantageous in a harsh environment having a high interference level occurring during the operation of the injection molding die, because such current-adaptive transmission is highly reliable.

[0016] The sensor element can be provided with a TEDS in which TEDS digital data regarding the sensor element and / or the measurement point is stored. Next, the data acquisition device includes a read / write circuit designed to read digital data from the TEDS and / or write digital data to the TEDS. Thereby, it becomes possible to automatically provide digital data to the data acquisition device via the sensor element without a person inputting the digital data to the data acquisition device via special input means. Such digital data regarding the sensor element includes a sensor type, sensitivity, calibration data, and the like. Also, by automatically providing digital data, input errors in the input of digital data are avoided, and the quality and usability of the piezoelectric measurement device are improved.

[0017] The sensor element includes a piezoelectric element, the piezoelectric element generates electric charges under the influence of the measured pressure, and the electric charges flow into the inverting input of the operational amplifier. Regarding a particularly compact design of the measurement device, it is also advantageous that the operational amplifier and the feedback capacitor are arranged together with the piezoelectric element within a common housing of the sensor element.

[0018] The piezoelectric measurement device is preferably used to measure the cavity pressure that spreads within the injection molding die during operation and is appropriately designed for this purpose. In particular, this includes a design of the piezoelectric measurement device or the sensor element that can permanently withstand, without damage, an operating temperature that often exceeds 100°C and relatively high pressures.

[0019] Furthermore, the present invention relates to a method for operating a piezoelectric measuring device, in particular designed in the manner described above. Here, a measurement signal is generated by a sensor element in response to the pressure to be measured, the measurement signal is transmitted to a data acquisition device by a conductor element, and the data acquisition device acquires and evaluates the transmitted measurement signal. The sensor element comprises an operational amplifier having an inverting input and an output. The sensor element comprises a feedback capacitance arranged in parallel with the inverting input and the output of the operational amplifier. And the sensor element comprises a reset switching element arranged in parallel with the inverting input and the output of the operational amplifier. In addition, the data acquisition device provides a supply voltage for the sensor element. The method according to the invention is characterized in that the data acquisition device has a measurement cycle circuit which switches on the supply voltage for the sensor element in a first step before the start of the measurement cycle, the sensor element detects the presence of the supply voltage in a second step, and if the supply voltage is present before the start of the measurement cycle, it comprises a power-on reset logic which closes and then opens the reset switching element, and the measurement cycle circuit switches off the supply voltage for the sensor element in a fifth step after the completion of the measurement cycle.

[0020] A preferred development of the method according to the invention is used to measure the cavity pressure that spreads in the injection mold during operation. In a first step, a measurement cycle for measuring the cavity pressure is started, and the power supply voltage for the sensor element is provided by the measurement cycle circuit. Here, in a second step, the presence of the power supply voltage is detected by the reset logic in the power-on reset circuit, and then the power-on reset circuit closes the reset switching element for a predetermined period, and the feedback capacitance is discharged by the closed reset switching element. Thereafter, the power-on reset circuit opens the reset switching element again. In a third step, a measurement cycle for measuring the cavity pressure is executed over a certain period, during which the charge generated by the piezoelectric element is converted into a measurement signal by the operational amplifier, and the measurement signal is acquired and evaluated by the data acquisition device. When the measurement cycle is completed, the measurement cycle circuit turns off the power supply voltage for the sensor element in a fifth step.

[0021] Preferably, the data acquisition device has a blanking circuit, and the blanking circuit blanks the first measurement signal acquired by the data acquisition device in a fourth step to improve the measurement accuracy.

[0022] More preferably, the sensor element includes a TEDS in which TEDS digital data regarding the sensor element and / or the measurement point is stored, a first diode, and a second diode. In this case, the data acquisition device includes a read / write circuit and a read / write switching element. To start the read / write operation, in a 0th step, the read / write switching element is activated by the read / write circuit. A negative DC voltage is provided by the read / write circuit, and the negative DC voltage is applied to the conductor element, rendering the first diode non-conductive and the second diode conductive. The read / write circuit is designed to read digital data from the TEDS and / or write digital data to the TEDS. To end the read / write operation, the read / write switching element is deactivated by the read / write circuit.

[0023] Further advantages, features, and details of the present invention will become apparent from the following description of the preferred embodiments of the present invention and the drawings.

[0024] Further advantages, features, and details of the present invention will become apparent from the following description of the exemplary embodiments and the drawings.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0026] In the figures, the same elements, or elements having the same function respectively, are assigned the same reference numerals.

[0027] FIG. 1 shows a first embodiment of the piezoelectric measurement device 100, which is preferably used to measure the cavity pressure that spreads in an injection mold (not shown during operation). The injection mold can be used for injection molding of molded parts made of liquefiable materials such as plastics and metals.

[0028] In addition, it is explained that, for example, if the cycle time during which a signal is evaluated is short enough in the assembly process, the piezoelectric measurement device 100 can in principle also be used for other applications, such as force monitoring in such an assembly process.

[0029] The piezoelectric measurement device 100 includes a sensor element 10 disposed within a housing 14. The function of the sensor element 10 is to generate a measurement signal M regarding the measured cavity pressure.

[0030] The piezoelectric measurement device 100 includes a data acquisition device 12 disposed at a location different from the sensor element 10. The function of the data acquisition device 12 is to acquire the measurement signal M from the sensor element 10, evaluate the measurement signal M, and draw a conclusion regarding the cavity pressure from the evaluation.

[0031] The sensor element 10 is electrically connected to the data acquisition device 12. The electrical connection is established by the conductor element 13. Preferably, the conductor element 13 is a single-core cable having a single signal conductor. The conductor element 13 functions to transmit the measurement signal M from the sensor element 10 to the data acquisition device 12 and to provide the power supply voltage U to the sensor element 10 via the data acquisition device 12. The housing 14 of the sensor element 10 and the data acquisition device 12 have the same electrical mass 15. Preferably, the housing 14 of the sensor element 10 and the data acquisition device 12 are present on the same electrical mass 15 via an injection molding die. The electrical mass 15 forms an electrical reference potential for the transmission of the measurement signal M and the provision of the power supply voltage U. The conductor element 13 may also be a two-core cable including a signal conductor and a mass conductor connected to the electrical mass 15. The signal conductor and the mass conductor are made of a conductive material such as copper.

[0032] The sensor element 10 includes a piezoelectric element 18. The cavity pressure to be measured acts as a force on the piezoelectric element 18, and the piezoelectric element 18 generates piezoelectric charges under the action of the force. In addition to the piezoelectric element 18, the sensor element 10 also includes an operational amplifier 20 having an inverting input and an output. The charges generated by the piezoelectric element 18 flow into the inverting input of the operational amplifier 20, which is marked with a minus sign in FIGS. 1 to 4. In FIGS. 1 to 4, the non-inverting input of the operational amplifier 20 is marked with a plus sign. Further, a feedback capacitor 22 that functions as an integrator arranged in parallel with the inverting input and the output of the operational amplifier 20 is provided. The operational amplifier 20 and the feedback capacitor 22 form a charge amplifier that converts the charges into the measurement signal M. The measurement signal M can be tapped at the output of the operational amplifier 20. The measurement signal M is a voltage signal and typically has an amplitude of several volts, for example, 0 V to +10 V, and a dynamics of several kHz.

[0033] In addition, the sensor element 10 includes a power-on reset circuit 25 including a reset logic 26. The power-on reset circuit 25 acts on a reset switching element 27 arranged in parallel with the feedback capacitor 22 and functions to discharge the feedback capacitor 22 in the closed position.

[0034] In the first embodiment of the piezoelectric measuring device 100 according to FIG. 1, the measurement signal M is transmitted from the sensor element 10 to the data acquisition device 12 as a voltage-adapted voltage signal. Further, the data acquisition device 12 is designed to provide a power supply voltage U for the sensor element 10 via the conductor element 13. For this purpose, the data acquisition device 12 has a voltage supply 30 having a positive DC voltage typically in the range of +18V to +30V, which is coupled to the conductor element 13 via a constant current regulating diode 36, and the power supply voltage U can be switched via a voltage supply switching element 32. The activation or operation (opening and closing) of the voltage supply switching element 32 is performed by the measurement cycle circuit 35.

[0035] Next, the operation of the piezoelectric measuring device 100 for detecting the cavity pressure of the injection molding die will be described in detail with reference to the flowchart of FIG. 5.

[0036] The measurement cycle for measuring the cavity pressure is started by first appropriately activating the measurement cycle circuit 35 and closing the voltage supply element 32 to provide the power supply voltage U for the sensor element 10 in the first step S1. The measurement cycle circuit 35 and the voltage supply element 32 are operably connected to each other as shown by the dashed lines in FIGS. 1 to 4.

[0037] The power supply voltage U is provided to the sensor element 10 via the conductor element 13. In the second step S2, the switching on or presence of the power supply voltage U in the sensor element 10 is detected here by the reset logic 26. Thereby, the power-on reset circuit 25 closes the reset switching element 27 for a predetermined period in order to discharge the feedback capacitor 22. For this purpose as well, the power-on reset circuit 25 and the reset switching element 27 are operatively connected to each other as shown by the dotted line in FIGS. 1 to 4. Thereafter, the reset switching element 27 is opened again by the power-on reset circuit 25.

[0038] Here, in the third step S3, the actual measurement cycle is carried out during a predetermined period, and the charge generated by the piezoelectric element 18 is converted into a measurement signal M by the operational amplifier 20. The measurement signal M is transmitted from the sensor element 10 to the data acquisition device 12 via the conductor element 13 and is acquired and evaluated by the data acquisition device 12.

[0039] The data acquisition device 12 optionally comprises a damping circuit 40. The damping circuit 40 comprises a signal input, a command input, and a signal output. Via the signal input, the damping circuit 40 is connected to the conductor element 13. Via the command input shown as a dashed line in FIGS. 1 to 4, the damping circuit 40 can be activated by the measurement cycle circuit 35. In an optional fourth step S4, the damping circuit 40 receives the measurement signal M via its signal input. Thus, the first measurement signal M acquired by the data acquisition device 12 in the measurement cycle is received and damped by the damping circuit 40. The damping circuit 40 outputs the damped measurement signal as a voltage signal 60 via the signal output. During damping, the level of the first measurement signal M is set to 0V.

[0040] Thereafter, the voltage signal 60 is evaluated during the operation of the injection molding machine, in particular during a measurement cycle typically lasting up to one minute at most.

[0041] To end the measurement cycle, in a fifth step S5, the power supply voltage U is switched off again via the measurement cycle circuit 35 and the voltage supply switching element 32.

[0042] The second embodiment of the piezoelectric measuring device 100 shown in FIG. 2 is largely based on the first embodiment of the piezoelectric measuring device 100 according to FIG. 1. Therefore, for the sake of avoiding repetition, please refer to its description. In the following, only the differences between the second embodiment of the piezoelectric measuring device 100 according to FIG. 2 and the first embodiment of the piezoelectric measuring device 100 according to FIG. 1 will be described.

[0043] Therefore, in the second embodiment of the piezoelectric measuring device 100 according to FIG. 2, the measurement signal M is current-matched and transmitted as a current signal from the sensor element 10 to the data acquisition device 12. For this purpose, the sensor element 10 comprises a 4..20 mA transmitter 23 and a current interface 24. The 4..20 mA transmitter 23 is connected to the output of the operational amplifier 20. The 4..20 mA transmitter 23 is designed to convert the voltage signal provided by the operational amplifier 20 into a current signal. The voltage signal is converted into a current signal in proportion to its magnitude. For example, a voltage signal of 0 V is converted into a current signal of 4 mA, and a voltage signal of 10 V is converted into a current signal of 20 mA. The 4..20 mA transmitter 23 is connected to the current interface 24. And the current interface 24 is connected to the conductor element 13. The current signal can be transmitted to the data acquisition device 12 via the current interface 24 and the conductor element 13.

[0044] The data acquisition device 12 includes a shunt element 41 connected downstream of the voltage supply source 30 and an additional operational amplifier 42. The shunt element 41 and the additional operational amplifier 42 are designed to convert the transmitted current signal back into a voltage signal. The current signal flows into the inverting input of the additional operational amplifier 42, which is marked with a minus sign as the symbol. The non-inverting input of the additional operational amplifier 40 is marked with a plus sign as the symbol. The voltage signal can be tapped at the output of the additional operational amplifier 40. Also, during reconversion, the current signal is converted into a voltage signal in proportion to its magnitude. For example, a 4 mA current signal is converted into a 0 V voltage signal, and a 20 mA current signal is converted into a 10 V voltage signal.

[0045] The two further embodiments of the piezoelectric measurement device 100 shown in FIGS. 3 and 4 also essentially correspond to the first two embodiments of the piezoelectric measurement device 100 according to FIGS. 1 and 2. For their descriptions, reference is made thereto. In the following, only the differences between the two further embodiments of the piezoelectric measurement device 100 according to FIGS. 3 and 4 compared with the first two embodiments of the piezoelectric measurement device 100 according to FIGS. 1 and 2 will be described.

[0046] Therefore, the sensor element 10 further includes a transducer electronic data sheet (TEDS) indicated by reference numeral 21. TEDS 21 is a data storage element in which digital data D for the sensor element 10 and / or the measurement point is stored. The digital data D for the sensor element 10 includes the sensor type, sensitivity, calibration data, etc. TEDS 21 has an input and an output. The TEDS 21 is electrically connected to the input to the conductor element 13, and the TEDS 21 is electrically connected to the output to the electrical mass 15.

[0047] In addition, the data acquisition device 12 includes a read / write circuit 50 and a read / write switching element 52. The read / write circuit 50 is designed to read digital data D from the TEDS 21 and / or write the digital data D to the TEDS 21 in a read / write operation. For this purpose, the read / write switching element 52 can be activated and deactivated by the read / write circuit 50 via a command input shown as a dashed line in FIGS. 3 and 4. In the activated state according to FIGS. 3 and 4, the read / write circuit 50 is electrically connected to the conductor element 13. In the deactivated state, the power supply source 30 is electrically connected to the conductor element 13. A first diode 28 is disposed between an end of the conductor element 13 and the operational amplifier 20. A second diode 29 is disposed between an input of the TEDS 21 and the conductor element 13.

[0048] During the measurement cycle, the power supply voltage U provided by the voltage supply source 30 exists as a positive DC voltage on the conductor element 13, the first diode 28 is conductive, and the second diode 29 is non-conductive. Then, the second diode 29 does not allow current to flow from the conductor element 13 to the TEDS 21. Therefore, during the measurement cycle, the TEDS 21 is electrically insulated from the operational amplifier 20 and the data acquisition device 12 and cannot affect the measurement cycle.

[0049] The read / write operation is optional. In the flowchart according to FIG. 5, the read / write operation is performed in the 0th step S0. The 0th step S0 can be performed before the other steps S1 to S5 of the method V. To start the read / write operation, the read / write switching element 52 is activated by the read / write circuit 50. Here, the negative DC voltage U* provided by the read / write circuit 50 is applied to the conductive element 13, making the first diode 28 non-conductive and the second diode 29 conductive. Then, the first diode 28 does not allow current to flow from the conductive element 13 to the operational amplifier 20. Therefore, during the read / write operation, the operational amplifier 20 is electrically insulated from the data acquisition device 12 and cannot affect the read / write operation. Here, the read / write circuit 50 can read digital data D from the TEDS 21 and / or write digital data D to the TEDS 21. To end the read / write operation, the read / write switching element 52 is deactivated by the read / write circuit 50.

[0050] The four embodiments of the piezoelectric measurement device 100 described above can be modified or changed in various ways without departing from the spirit of the present invention.

Description of Reference Numerals

[0051] 10 Sensor element 12 Data acquisition device 13 Conductor element 14 Housing 15 Electrical mass 18 Piezoelectric element 20 Operational amplifier 21 TEDS 22 Feedback capacitance 23 Current interface 24 4..20mA transmitter 25 Power-on reset circuit 26 Reset logic 27 Reset switching element 28 First diode 29 Second diode 30 Voltage supply source 32 Voltage supply switching element 35 Measurement cycle circuit 36 Constant current regulating diode 40 Ballast circuit 41 Shunt element 42 Additional operational amplifier 50 Read / write circuit 52 Read / write switching element 60 Voltage signal 100 Piezoelectric measuring device D Digital data M Measurement signal U Power supply voltage U* Negative DC voltage V Method S0 Step 0 S1 Step 1 S2 Step 2 S3 Step 3 S4 Step 4 S5 Step 5

Claims

1. A piezoelectric measurement device (100), comprising a sensor element (10) designed to generate a measurement signal (M) for the pressure to be measured, and a conductor element (13) for transmitting the measurement signal (M) to a data acquisition device (12), wherein the data acquisition device (12) is designed to acquire and evaluate the transmitted measurement signal (M). The sensor element (10) comprises an operational amplifier (20) with an inverting input and an output, and the sensor element (10) comprises a feedback capacitor (22) arranged in parallel with the inverting input and the output of the operational amplifier (20). The sensor element (10) comprises a reset switching element (27) arranged in parallel with the inverting input and the output of the operational amplifier (20). The data acquisition device (12) is further configured to provide a power supply voltage (U) for the sensor element (10), and the data acquisition device (12) is provided with a measurement cycle circuit (35) configured to switch on the power supply voltage (U) for the sensor element (10) before the start of a measurement cycle and to switch off the power supply voltage (U) after the completion of the measurement cycle. The sensor element (10) comprises a power-on reset circuit (25) designed to detect the presence of the power supply voltage (U) and, if the power supply voltage (U) is present before the start of a measurement cycle, to close and then reopen the reset switching element (27). A piezoelectric measurement device (100) characterized by the above.

2. The piezoelectric measurement device (100) according to claim 1, characterized in that the measurement cycle circuit (35) is designed to switch on or off a voltage supply source (30) for the sensor element (10) by means of a voltage supply switching element (32).

3. The piezoelectric measurement device (100) according to claim 1 or 2, characterized in that the power-on reset circuit (25) is designed to operate the reset switching element (27) to discharge the feedback capacitor (22).

4. The piezoelectric measurement device (100) according to claim 1, characterized in that the data acquisition device (12) is provided with a dead-band circuit (40) designed to discard the first measurement signal (M) transmitted from the sensor element (10) to the data acquisition device (12).

5. The piezoelectric measurement device (100) according to claim 3, characterized in that the power-on reset circuit (25) comprises a power-on reset logic (26) that closes the reset switching element (27) to discharge the feedback capacitance (22) after a prescribed time exceeds a predetermined voltage value, and then opens it again.

6. The piezoelectric measurement device (100) according to claim 1, characterized in that the conductor element (13) is a single-core cable having a single signal conductor.

7. The sensor element (10) comprises a 4..20 mA transmitter (23) and a current interface (24), the 4..20 mA transmitter (23) is connected to the output of the operational amplifier (20), and is designed to convert the measurement signal (M) provided by the operational amplifier (20) as a voltage signal into a current signal, the 4..20 mA transmitter (23) is connected to the current interface (24), the current interface (24) is connected to the conductor element (13), and the current signal can be transmitted to the data acquisition device (12) via the current interface (24) and the conductor element (13). The piezoelectric measurement device (100) according to claim 1 or 2, characterized in that.

8. The data acquisition device (12) comprises a shunt element (41) downstream of the voltage supply source (30) and an additional operational amplifier (42), and the shunt element (41) and the additional operational amplifier (42) are designed to convert the transmitted current signal back into a voltage signal. The piezoelectric measurement device (100) according to claim 7, which quotes claim 2, characterized in that.

9. The sensor element (10) comprises a TEDS (21) in which TEDS (21) digital data (D) regarding the sensor element (10) and / or the measurement point is stored, and the data acquisition device (12) is designed to read digital data (D) from the TEDS (21) and / or write digital data (D) to the TEDS (21). The piezoelectric measurement device (100) according to claim 1, characterized in that it comprises a read / write circuit (50).

10. The piezoelectric measurement device (100) according to claim 1, wherein the sensor element (10) includes a piezoelectric element (18), the piezoelectric element (18) generates an electric charge under the influence of the pressure to be measured, the electric charge flows into the inverting input of the operational amplifier (20), and the operational amplifier (20) and the feedback capacitance (22) are arranged together with the piezoelectric element (18) within a common housing (14) of the sensor element (10).

11. The piezoelectric measurement device (100) according to claim 1, characterized in that the piezoelectric measurement device (100) is designed to measure a cavity pressure that spreads within an injection molding die during operation.

12. A method (V) for operating a piezoelectric measurement device (100) designed as described in claim 1, wherein a measurement signal (M) is generated by a sensor element (10) with respect to the pressure to be measured, the measurement signal (M) is transmitted by a conductor element (13) to a data acquisition device (12), the data acquisition device (12) detects and evaluates the transmitted measurement signal (M), the sensor element (10) includes an operational amplifier (20) having an inverting input and an output, the sensor element (10) includes a feedback capacitance (22) arranged in parallel with the inverting input and the output of the operational amplifier (20), the sensor element (10) includes a reset switching element (27) arranged in parallel with the inverting input and the output of the operational amplifier (20), the data acquisition device (12) further provides a power supply voltage (U) for the sensor element (10), the data acquisition device (12) includes a measurement cycle circuit (35) that switches on the power supply voltage (U) for the sensor element (10) before the start of a measurement cycle in a first step (S1), the sensor element (10) detects the presence of the power supply voltage (U) in a second step (S2), and when the power supply voltage (U) is present, includes a power-on reset circuit (25) that closes and then opens the reset switching element (27) before the start of the measurement cycle, and the measurement cycle circuit (35) switches off the power supply voltage (U) for the sensor element (10) in a fifth step (S5) after the completion of the measurement cycle.

13. The method (V) is used to measure the cavity pressure that spreads in the injection mold during operation, whereby a measurement cycle for measuring the cavity pressure is started. In the first step (S1), the power supply voltage (U) for the sensor element (10) is provided by the measurement cycle circuit (35). In the second step (S2), the presence of the power supply voltage (U) is detected by the reset logic (26) in the power-on reset circuit (25). Thereafter, the power-on reset circuit (25) closes the reset switching element (27) for a predetermined period, and the feedback capacitance (22) is discharged by the closed reset switching element (27). The power-on reset circuit (25) then opens the reset switching element (27) again. In the third step (S3), the measurement cycle for measuring the cavity pressure is executed over a specific period, during which the charge generated by the piezoelectric element (18) is converted into the measurement signal (M) by the operational amplifier (20), and the measurement signal (M) is detected and evaluated by the data acquisition device (12). After completion of the measurement cycle, the measurement cycle circuit (35) switches off the power supply voltage (U) for the sensor element (10) in the fifth step (S5). The method (V) according to claim 12, characterized in that.

14. The method (V) according to claim 13, characterized in that the data acquisition device (12) comprises a deadband circuit (40), and the deadband circuit (40) deadbands the first measurement signal (M) acquired by the data acquisition device (12) in the fourth step (S4).

15. The sensor element (10) includes a TEDS (21) in which TEDS (21) digital data (D) regarding the sensor element (10) and / or a measurement point is stored, a first diode (28), and a second diode (29). The data acquisition device (12) includes a read / write circuit (50) and a read / write switching element (52). In order to start a read / write operation, in a zero-th step (S0), the read / write switching element (52) is activated by the read / write circuit (50), and a negative DC voltage (U*) is provided by the read / write circuit (50). The negative DC voltage (U*) is applied to the conductor element (13), making the first diode (28) non-conductive and the second diode (29) conductive. The read / write circuit (50) is designed to read digital data (D) from the TEDS (21) and / or write digital data (D) to the TEDS (21). In order to end the read / write operation, the read / write switching element (52) is deactivated by the read / write circuit (50). The method (V) according to any one of claims 12 to 14, characterized in that.

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