Reading a 4 cable Pressure Transducer

Using Arduino Project Guidance
1

Hi,

I am currently trying to read a Kulite XCL-100 with an Arduino. The sensor requires a 10V excitation and outputs a 0-100mV signal. I am then amplifying this signal with a LM358 op amp with a gain of 49.66 to a 0-5V signal. Unfortunately, I believe there may be a grounding issue since the output signal is oscillating between around 30000 pascals (0.9V).

I may be wrong, but this seems a little odd to me. I have attached the Arduino serial plotter and the circuit diagram I have set up.

Thanks for any advice,

Tom

PT Circuit.PNG
PT Circuit.PNG692×571 42.7 KB

PT graph.PNG
PT graph.PNG1611×636 86.9 KB

2

Please post a real circuit diagram of the amplifier.

You undoubtedly need an instrumentation amplifier for that sensor. One tutorial at Stay Out of Deep Water When Designing with Bridge Sensors | Analog Devices

3

ground the negative excite lead to the sensor

4

Sensor seems to be a common wheatstone bridge.
The 10volt excitation is not required.
Dump the LM358, and use a HX711 breakout board.
Leo..

5

Thanks for the responses. I have attached the diagram of the op amp.

If I ground the sensor to the supply then the sensor no longer produces a signal that varies with pressure.

The pressure transducer has a standard wheatstone bridge configuration but according to the manufacturer requires a 10V excitation.

My theory with the design was that the signal just needed amplifying. But I assume that the output needs to be compared. I have tried using a differential amplifier setup but have still had no luck.

Thanks,
Tom

Op Amp.PNG

6

red and black are positive and negative excite

green and white are positive and negative output

output is floating, neither output goes to ground. outputs go to an instrumentation amplifier, which is rather more complex than an op amp:

( Red-Grn ) X ( Blk- Wht ) resistance should be within 2% of
( Blk-Grn ) X ( Red-Wht )

linearity of Kulite XC transducers is remarkable; about .01%

7

Hi,

What are the differences between R1, R2, R3 and Rgain?

I need to amplify the signal by about 50.

Thanks,
Tom

8

I got that from the wikipedia "instrumentation amplifier" page

search term: "instrumentation amplifier schematic" will keep you busy for a while.

see also "instrumentation amplifier balance circuit"

9

If you used the Arduino's 1.1 volt internal reference, you would only need amplification of about 11 or less, 100 mV to 1.1V.

10

How many A/D values (different pressure levels/steps) are you expecting from that setup.
With the LM358 and Arduino's A/D from post#0 that would be about 700.
With an instrumentation amp ? Depends on he supply and output swing of the third opamp.
Better re-consider what I said in post#3.
Leo..