Hi group


This is a pressure sensor signal modulation board.(Please see the attached "PCB" file.)
It comes from inside the flow module.(Please see the attached image "PCB3".)
I have drawn the schematic diagram of the actual PCB. Please see the attached "Schematic diagram - Full version".

The pressure sensor 125PC05D1 is used in conjunction with this signal conditioning board.The pressure sensor 125PC05D1 operates at a voltage of 0-10VDC and a current of 0-2mA.Input or output impedance approximately 5K ohms.

The 125PC05D1 pressure sensor exhibits severe zero-point drift.So I had no choice but to replace it.

I've decided to try replacing the 125PC05D1 with an MPX2010DP pressure sensor. The MPX2010DP pressure sensor operates at 10V and draws 6mA. Its input impedance is 1.7998K ohms, and its output impedance is 1.7435K ohms.

R1123(VB SET):Used to adjust the bias voltage, which is the operating voltage of the pressure sensor V+ and V- (typically 10,000V).
R1116(ZERO):Used to adjust the voltage between S+ and GND or between S- and GND to 0.000V.
R1111(XDBAL):Used to adjust the voltage between S+ and S- to 0.000V.
R1102(NULL):Used to adjust the Vout （HI-LO voltage）output voltage to 0 ± 0.005Vdc(Adjust according to the requirements in the service manual.)
R1109(TC):No adjustments have been made yet; it appears to be used to adjust temperature drift compensation, but it's unclear exactly how to adjust it.


Since the original pressure sensor signal modulation board used a 125PC05D1 pressure sensor, and I have now replaced it with an MPX2010DP pressure sensor, how should I modify the original signal modulation board to make the MPX2010DP pressure sensor work properly? Furthermore, how should I configure the bias circuit, zero-adjustment circuit, differential amplifier circuit, gain circuit, etc., to meet the original parameter requirements?

Another question is, how can we keep the Vout output voltage constant (in the zero-pressure input state)?


https://i.postimg.cc/9FsYrnXF/sensor-125pc05d1.jpg
https://i.postimg.cc/02h0bB5r/sensor-125pc05d1-2.jpg

 

"Regarding the inherent thermal drift phenomenon in silicon piezoresistive bridge circuits: self-heating and ambient temperature both affect zero-point offset." — I conducted a comparative test.

Please watch the test video below.

These are two identical RT-200 analyzers.

The one on the left belongs to my friend. His RT-200 hardware is newer (vertically mounted, pressure sensor replaced with NPH-8-030DH). The one on the right is mine; I installed a new MPX2010DP pressure sensor on it. (The test points are all high and low voltages, i.e., the output voltage of the signal amplifier board. Inputting "30" on the main unit achieves the same effect, i.e., displaying one of the output voltage values.) As can be seen from the video, the zero-drift car on the left is significantly better than the car on the right. (I did not find any difference by analyzing the pressure sensor datasheet; I have taken clear comparison photos.)

Can I adjust the zero-point drift of the RT-200 main unit on the right to be the same as the one on the left?

 

Please see the image.

 

Hi @daisizhou
Welcome to ACC.
Check this link for advice on the [tc] adjustment
E

https://www.google.com/search?clien...rential+pressure+sensor+circuit+tc+adjustment

clip:
AI Overview
The MPX2010DP is a silicon piezoresistive differential pressure sensor that includes on-chip laser trimming for span, offset, and temperature compensation (TC) over a range of 0°C to 85°C
. While it is pre-compensated, precise, temperature-stable applications may require external signal conditioning, typically involving an instrumentation amplifier (like the INA125 or INA126) to boost the 25mV full-span output and to trim residual zero-point offset or TC errors.
1. MPX2010DP Internal Compensation

On-Chip TC: The sensor uses a monolithic silicon diaphragm with an integrated thin-film resistor network, allowing for temperature compensation of both span and offset without external components in many applications.
Ratiometricity: The output is ratiometric, meaning the span and offset change proportional to the supply voltage, so a stable 10V DC power supply is critical for performance.

2. External TC Adjustment Circuit Techniques
If the internal compensation is insufficient for high-precision, wide-temperature applications, or if replacing an old sensor with a different, non-compensated one, external compensation may be necessary.

Bridge Supply Voltage Adjustment: A common method to adjust temperature coefficient of span (TCS) is by using a thermistor or active temperature sensor (like LM334) in the voltage regulator circuit feeding the Wheatstone bridge.
Active Instrumentation Amplifier (INA125/INA126):
Connect Pin 2 (
) and Pin 4 (
) of the MPX2010DP to the inputs of an instrumentation amplifier.
Zero/Offset Calibration: Connect a potentiometer to the Ref pin of the instrumentation amplifier to zero the output at 0 Pa differential pressure.
Gain/Span Adjustment: Use the gain-setting resistor (
) on the amplifier to set the full-scale voltage output to match the ADC range (e.g., 0–5V).
Component Selection for Stability: Use high-precision resistors (1% or better) and low-drift components in the amplification stage to prevent introducing temperature-dependent errors.

Added: cleaned up your circuit images.

 

Hi @daisizhou
Welcome to ACC.
Check this link for advice on the [tc] adjustment
E

https://www.google.com/search?clien...rential+pressure+sensor+circuit+tc+adjustment

clip:
AI Overview
The MPX2010DP is a silicon piezoresistive differential pressure sensor that includes on-chip laser trimming for span, offset, and temperature compensation (TC) over a range of 0°C to 85°C
. While it is pre-compensated, precise, temperature-stable applications may require external signal conditioning, typically involving an instrumentation amplifier (like the INA125 or INA126) to boost the 25mV full-span output and to trim residual zero-point offset or TC errors.
1. MPX2010DP Internal Compensation

On-Chip TC: The sensor uses a monolithic silicon diaphragm with an integrated thin-film resistor network, allowing for temperature compensation of both span and offset without external components in many applications.
Ratiometricity: The output is ratiometric, meaning the span and offset change proportional to the supply voltage, so a stable 10V DC power supply is critical for performance.

2. External TC Adjustment Circuit Techniques
If the internal compensation is insufficient for high-precision, wide-temperature applications, or if replacing an old sensor with a different, non-compensated one, external compensation may be necessary.

Bridge Supply Voltage Adjustment: A common method to adjust temperature coefficient of span (TCS) is by using a thermistor or active temperature sensor (like LM334) in the voltage regulator circuit feeding the Wheatstone bridge.
Active Instrumentation Amplifier (INA125/INA126):
Connect Pin 2 (
) and Pin 4 (
) of the MPX2010DP to the inputs of an instrumentation amplifier.
Zero/Offset Calibration: Connect a potentiometer to the Ref pin of the instrumentation amplifier to zero the output at 0 Pa differential pressure.
Gain/Span Adjustment: Use the gain-setting resistor (
) on the amplifier to set the full-scale voltage output to match the ADC range (e.g., 0–5V).
Component Selection for Stability: Use high-precision resistors (1% or better) and low-drift components in the amplification stage to prevent introducing temperature-dependent errors.

Added: cleaned up your circuit images.

Thanks

If I don't change the R1118 resistor, that is, if I continue to use the 17.8K resistor, then the voltage between V+ and V- of the pressure sensor is only 1.3161V. 10÷((0.475+17.8×0.475÷0.475)÷1.8−17.8÷6.97)≈1.28


To enable the MPX2010DP to operate at 10.000V DC, I changed the value of resistor R1118 from 17.8K to approximately 1.8K.
Then, by adjusting R1123 (VBSET), the pressure sensor operating voltages V+ and V- can indeed be adjusted to 10.000V.
However, the pressure sensor's S+ and GND, or S- and GND, cannot be adjusted to 0.000V by adjusting R1116 (ZERO).
I don't know why(I'm not sure if there are any other resistor values that need adjustment, and the Vout output still has a zero-point drift problem, even though it's only been reduced.).

 

I once tried to use a similar "semiconductor strain gage" sensor. A stable zero point was not possible if the sensor or the mounting temperature changed at all. My conclusion was that they can only be used for AC coupled applications, such as sensing pump pressure ripple. They als sense mechanical vibration a bit.