Hello,
I got myself into a bit of a pickle. Long story short, I have a few 0-1000 Pa differential sensors, plus a circuit that turns this into a 0-10VDC signal. The supply voltage is 24 VDC.
I would actually need 10V to be 250 Pa or so instead. I could order the same sensors again, which would mean binning the current ones and waiting for a few months for them to arrive, but because all the sensors seem to actually use the same 0-1 kPa sensor instead, I am suspecting that it should be possible to control the gain by changing a resistor on the board.
Here are the pictures of both sides of the circuit board:
You can also find the the datasheet for the pressure sensor in the attachments.
The 16 pin IC is a mystery to me. It is marked as 3094AS, but I can not find any information about it. Usually a differential pressure sensor circuit would have some sort of op-amp, so I would hazard a guess it is some sort of an instrumentation opamp. Those usually have external gain resistors... which is what I am hoping for here.
The wire colors that come into the board from the sensor are as follows:
S+ - yellow
S- - white
I+ - red
I- blue.
Now, S+ is connected through a 49.9k resistor to Pin 5 of the IC and S- is connected through a 49.9k resistor to Pin 6. Measuring the resistance between S+ or S- and ground I get 3.2k (or 2.2k to I-, as there's a 1k resistor from I- to GND), as expected the S+ resistance goes down when pressure is applied to the higher pressure port of the sensor and S- resistance goes up by the same amount.
The output is a lot less clear to me. I thought initially it was fairly simple, as it goes through R10 to Pin 13 on the IC, and then it would mean that the IC is outputting the 0-10V signal, with R10 (2.2k) being a current limiter and R11 (2k) being a pulldown resistor, but then I noticed that T3 (BFS20 NPN) is also connected to the output directly, and this is where my knowledge is insufficient to make heads or tails of anything anymore.
I thought about just changing the I- 1k resistor to ground for a bigger one, but a quick simulation with LTSpice seems to be telling me, that this is probably a stupid idea.
So I figured before I bin a few hundred euros worth of sensors, I'd ask for advice. Most likely one of the resistors (or a combination) are gain resistors on the op-amp and by changing them it will be simple enough to alter the output gain.
I'll also note that the absolute reading of the sensor is actually completely irrelevant. The sensor is meant to control the pressure in my ventilation system, and the target pressures are found empirically anyway by equalizing intake and exhaust using a flow meter, then noting down the pressures. After that there is a closed loop PI controller in the control unit. The problem is that the signal is too low for the control, and I have no control over the software in the control unit.
If anyone feels like helping out, it'd be most appreciated.
I got myself into a bit of a pickle. Long story short, I have a few 0-1000 Pa differential sensors, plus a circuit that turns this into a 0-10VDC signal. The supply voltage is 24 VDC.
I would actually need 10V to be 250 Pa or so instead. I could order the same sensors again, which would mean binning the current ones and waiting for a few months for them to arrive, but because all the sensors seem to actually use the same 0-1 kPa sensor instead, I am suspecting that it should be possible to control the gain by changing a resistor on the board.
Here are the pictures of both sides of the circuit board:
You can also find the the datasheet for the pressure sensor in the attachments.
The 16 pin IC is a mystery to me. It is marked as 3094AS, but I can not find any information about it. Usually a differential pressure sensor circuit would have some sort of op-amp, so I would hazard a guess it is some sort of an instrumentation opamp. Those usually have external gain resistors... which is what I am hoping for here.
The wire colors that come into the board from the sensor are as follows:
S+ - yellow
S- - white
I+ - red
I- blue.
Now, S+ is connected through a 49.9k resistor to Pin 5 of the IC and S- is connected through a 49.9k resistor to Pin 6. Measuring the resistance between S+ or S- and ground I get 3.2k (or 2.2k to I-, as there's a 1k resistor from I- to GND), as expected the S+ resistance goes down when pressure is applied to the higher pressure port of the sensor and S- resistance goes up by the same amount.
The output is a lot less clear to me. I thought initially it was fairly simple, as it goes through R10 to Pin 13 on the IC, and then it would mean that the IC is outputting the 0-10V signal, with R10 (2.2k) being a current limiter and R11 (2k) being a pulldown resistor, but then I noticed that T3 (BFS20 NPN) is also connected to the output directly, and this is where my knowledge is insufficient to make heads or tails of anything anymore.
I thought about just changing the I- 1k resistor to ground for a bigger one, but a quick simulation with LTSpice seems to be telling me, that this is probably a stupid idea.
So I figured before I bin a few hundred euros worth of sensors, I'd ask for advice. Most likely one of the resistors (or a combination) are gain resistors on the op-amp and by changing them it will be simple enough to alter the output gain.
I'll also note that the absolute reading of the sensor is actually completely irrelevant. The sensor is meant to control the pressure in my ventilation system, and the target pressures are found empirically anyway by equalizing intake and exhaust using a flow meter, then noting down the pressures. After that there is a closed loop PI controller in the control unit. The problem is that the signal is too low for the control, and I have no control over the software in the control unit.
If anyone feels like helping out, it'd be most appreciated.
Attachments
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