I need to create a circuit that will simulate a differential pressure sensor, like shown here:
http://allsensors.com/datasheets/DS-0102_Rev_A.pdf
There’s an equivalent circuit in the PDF, but I’m not experienced enough to know what components I’d need to put it together.
I appreciate any help in solving this.
Thanks,
Bob
The sensor outputs a voltage related to the pressure. Why do you want to build the “equivalent circuit” and what do you want it to do?
This question is probably better suited for the ‘projects’ forum. This forum is geared more toward designing PCBs (i.e. board layout), not really circuit design. Not a sin, just may not get your question in front of the audience you intended.
We’ll be able to better help you if you can give us more details as to what you’re trying to do. A simple variable voltage supply may be a sufficient simulator depending on what you’re doing.
dlotton:
This question is probably better suited for the ‘projects’ forum. This forum is geared more toward designing PCBs (i.e. board layout), not really circuit design. Not a sin, just may not get your question in front of the audience you intended.We’ll be able to better help you if you can give us more details as to what you’re trying to do. A simple variable voltage supply may be a sufficient simulator depending on what you’re doing.
Is there a simple way to move a topic to other forums, or do you start new one? The reason I thought posting here was correct is because I will ultimately create a PCB, but I do see now that this is more a project question.
The differential pressure sensors are expensive - $100/ea (I need to use 2), so I’d rather experiment with cheaper components. I am building an Arduino circuit to transmit sensor data using Bluetooth LE. Usage of the differential pressures in my design will actually see Port B go down by the same value as Port A goes up. So I’d think a pot could be used where a CW twist results in Port A voltage changing by, say, +2 mV and Port B changing by -2 mV. A CCW twist results in opposite.
The circuit also includes a temperature sensor (LM35), but I already have that working. I may include a humidity sensor - so a total of four sensors - each transmitting on separate analog pins. I’ll then create a shield that plugs into an Arduino Micro + BLE.
Thanks,
Bob
One method is to use two pressure sensors, one on each side. However you can run inot resolution/accuracy issues if the common mode pressure is very high and the pressure difference is very small. Also will need two ADC point for each DPIT.
dschlic1:
One method is to use two pressure sensors, one on each side. However you can run inot resolution/accuracy issues if the common mode pressure is very high and the pressure difference is very small. Also will need two ADC point for each DPIT.
I want to simulate the pressure sensor using a pot, so that I can twist it CW and CCW and transmit voltages (pressures) for code and circuit debugging before using an actual sensor. My problem is I only know about three-lead pots, and the sensor actually has four-leads. When I am done and my circuit actually works I will substitute an actual sensor on the PCB. So I need to know how to how to hook up a three-lead pot into a four-lead configuration that would simulate what a sensor would accomplish.
Thanks,
Bob
Moved to Projects forum, since you asked so nicely.
Thanks!
While the device seems to have 4 leads, the equivalent circuit uses only 3 of them. One is the supply voltage, 2 is the ground and 3 is the output voltage. Looks like a pot would be a very good simulator.carpenterdev:
I want to simulate the pressure sensor using a pot, so that I can twist it CW and CCW and transmit voltages (pressures) for code and circuit debugging before using an actual sensor. My problem is I only know about three-lead pots, and the sensor actually has four-leads.
Mee_n_Mac:
While the device seems to have 4 leads, the equivalent circuit uses only 3 of them. One is the supply voltage, 2 is the ground and 3 is the output voltage. Looks like a pot would be a very good simulator.carpenterdev:
I want to simulate the pressure sensor using a pot, so that I can twist it CW and CCW and transmit voltages (pressures) for code and circuit debugging before using an actual sensor. My problem is I only know about three-lead pots, and the sensor actually has four-leads.
The actual sensor does have 4 leads, so I want to make my board layout with 4 leads. I can take Vout and invert it and then set that to a separate Arduino pin. I’d set A1 to Vout and A2 to -Vout. See any problem with this?
Thanks,
Bob
You'll need additional circuitry and a - supply. To what end ? The sensor doesn't output a -Vout. For the absolute pressure types, it outputs a (nominal) voltage from 0.25 (zero pressure) to 4.0 V (full scale pressure). For differential types it outputs 2.25 V for 0 difference in pressure and that goes down to 0.25 V or up to 4.25 V, depending on which pressure is greater (A or B port) and how large that difference is. At least that's how I read the datasheet you supplied.\carpenterdev:
The actual sensor does have 4 leads, so I want to make my board layout with 4 leads. I can take Vout and invert it and then set that to a separate Arduino pin. I’d set A1 to Vout and A2 to -Vout. See any problem with this?
And an Arduino can only input and digitize + voltages.
Mee_n_Mac:
You'll need additional circuitry and a - supply. To what end ? The sensor doesn't output a -Vout. For the absolute pressure types, it outputs a (nominal) voltage from 0.25 (zero pressure) to 4.0 V (full scale pressure). For differential types it outputs 2.25 V for 0 difference in pressure and that goes down to 0.25 V or up to 4.25 V, depending on which pressure is greater (A or B port) and how large that difference is. At least that's how I read the datasheet you supplied.\carpenterdev:
The actual sensor does have 4 leads, so I want to make my board layout with 4 leads. I can take Vout and invert it and then set that to a separate Arduino pin. I’d set A1 to Vout and A2 to -Vout. See any problem with this?And an Arduino can only input and digitize + voltages.
Thanks for the help. I’ll build the circuit and try it out.
Bob
carpenterdev:
I need to create a circuit that will simulate a differential pressure sensor, like shown here:http://allsensors.com/datasheets/DS-0102_Rev_A.pdf
There’s an equivalent circuit in the PDF, but I’m not experienced enough to know what components I’d need to put it together.
I appreciate any help in solving this.
Thanks,
Bob
The equivalent circuit is an resistor Wheatstone bridge (google this) and a differential op-amp. Very simple to build in a circuit simulator (like LT SPICE) or a real circuit.
Just use a Pot for one of the resistor in the bridge then tweak values to obtain the data sheet’s output specs.
waltr:
carpenterdev:
I need to create a circuit that will simulate a differential pressure sensor, like shown here:http://allsensors.com/datasheets/DS-0102_Rev_A.pdf
There’s an equivalent circuit in the PDF, but I’m not experienced enough to know what components I’d need to put it together.
I appreciate any help in solving this.
Thanks,
Bob
The equivalent circuit is an resistor Wheatstone bridge (google this) and a differential op-amp. Very simple to build in a circuit simulator (like LT SPICE) or a real circuit.
Just use a Pot for one of the resistor in the bridge then tweak values to obtain the data sheet’s output specs.
I’ll build the Wheatstone bridge and Op-Amp circuit. I’ll put a 200K pot in place of one of the WSB resistors (I assume it doesn’t matter which?). For the Op-Amp I’ll use an NTE928M - I’ll wire it up as a comparator, like the All Sensors PDF shows.
Thanks for the help!
Bob
carpenterdev:
waltr:
carpenterdev:
I need to create a circuit that will simulate a differential pressure sensor, like shown here:http://allsensors.com/datasheets/DS-0102_Rev_A.pdf
There’s an equivalent circuit in the PDF, but I’m not experienced enough to know what components I’d need to put it together.
I appreciate any help in solving this.
Thanks,
Bob
The equivalent circuit is an resistor Wheatstone bridge (google this) and a differential op-amp. Very simple to build in a circuit simulator (like LT SPICE) or a real circuit.
Just use a Pot for one of the resistor in the bridge then tweak values to obtain the data sheet’s output specs.
I’ll build the Wheatstone bridge and Op-Amp circuit. I’ll put a 200K pot in place of one of the WSB resistors (I assume it doesn’t matter which?). For the Op-Amp I’ll use an NTE928M - I’ll wire it up as a comparator, like the All Sensors PDF shows.
Thanks for the help!
Bob
I finished the circuit and all is working well - I am able to control voltage from 2.8 mV to 3.13 V; which is a fairly normal pressure range I’d expect to see.
NOTES: For bridge I used calculator http://www.daycounter.com/Calculators/W … ator.phtml and found that Vin = 4.5 V, R1=990 ohms, R2=0 ohms, R3 = 148.4 ohms, with R4 as a 5K pot would provide voltage range of 0.25 V → 4.25 V.
For Op-Amp, I fed bridge +V to Non-Inverting Input A; bridge -V to Inverting Input A, set Vcc = 4.5V; Measured Output A.
Thanks,
Bob
Ok, great you got this working and thanks for posting your results.
I’m the OP, and have attached the details of my circuit. I am having a problem that I hope someone can help solve.
I wasn’t accurate in giving the specs for the circuit in the earlier post. The attachment shows the actual reality, which is that VOmin (measured) = 0.0015V (calculated is 0.34V), and VOmax (measured) = 3.19V (calculated is 4.37V).
My main problem is the circuit either produces 0.0015V or 3.19V and nothing in between. Is this expected for an OP Amp circuit? I’m using OP Amp NTE928M. About 10 degs CCW of pot rotation from CW stop produces the VOmin.
Also, why such a difference between the calculated voltages and the measured? Doesn’t seem like the ± 5% tolerance of the components would account for the big difference.
Thanks,
Bob
I highly recommend downloading LT Spice and simulating your circuit. It’s much, much easier to troubleshoot a model and you can easily change component values with a click.
That said. I think at least part of your problem is that R2 is 0, making your non-inverting input (+) always GND. Pretty much any voltage on the inverting input (-) is going to drive the output to GND since you don’t have a negative supply. If you had a negative supply on your op amp, the output would go negative. (Use LT Spice to simulate your circuit.)
I think you’re making this way too hard. Is it really necessary to try to replicate the bridge circuit? Aren’t you just trying to get a variable voltage into your ADC input to test some code?
dlotton:
I think at least part of your problem is that R2 is 0, making your non-inverting input (+) always GND…
Oops, Just realized your resistor diagram is mirrored left<=>right from the bridge on the equivalent ckt. Never mind that comment.
LT Spice!
There’s a lot going on that’s not right with your circuit. I’m not even sure where to start. For that circuit to work your amp needs to be a difference amp (which you could build out of your op amp). Ahhh, there’s a lot going on that I can’t really address here and now.
The circuit below will give you an output range approximately 0.25V-4.25V and the response will be pretty much linear with respect to the rotation of the pot wiper. Your circuit above, if it even worked, would not respond linearly to wiper rotation. R6 and R7 together represent your 5K pot. Vwiper represents the wiper output on the pot.
If you want to buffer the output of that circuit you can use your op amp to make a voltage follower, but it probably isn’t necessary feeding into your ADC input. A small cap on Vwiper would probably be sufficient (0.1uF) to reduce sampling noise.