08-01-2012 03:04 PM
So I'm looking to measure fluid pressures on the compound range from -100 to 400 mmHg, and I'm wondering if I can hook up the transducer found here to one of the NI C-Series modules. I've done a bit of reading on the forum and NI website, and it appears that the 9237 is capable of supplying the excitation current as well as reading output from most pressure transducers. My understanding is that most pressure sensors have 3 or 4-wire cables, but the schematic I've been given for plug coming from this transducer has an 8-pin DIN connector with the following pin labels/features:
1: Excitation (+)
2: Signal (-)
3: Signal (+)
4: Excitation (-)
5: 220 kOhm to pin 8
8: See pin 5
Other information given is as follows:
Pressure Range: -80 to +380 mmHg
Input Impedance: 3000 Ohms
Output Impedance: 300 Ohms
Excitation: 0-9 V DC
Sensitivity: 5 uV/V/mmHg
I would like to know if I can use this with a NI CompactDAQ system, which module would be best suited for this, and how I might wire this in. If this is not suitable, does anybody have any suggestions as to other transducers that work in this range and could be used? I'm fairly certain I understand the usual wiring setup for transducers, but this seems a bit different, so I'm worried it's some kind of proprietary setup.
I apologize ahead of time if this has been answered previously, but I searched for a while and could find nothing.
Thanks ahead of time for any help you can provide.
08-02-2012 06:23 PM
There are a few things to consider with this device. Do you happen to have more information on the 200K resistor mentioned in the DIN pin out? I'm also interested if this is a half, full, or quarter bridge device (and what kind). You provided some great information about the pin out and specs, but the product page you linked didn't have a lot more details (or the details you mentioned).
To answer your first question - yes, the 9237 will be your best bet for working with this sensor.
You also are right that the output from the sensor should be fine for the 9237. It shouldn't exceed 1.9mV/V (5uV/V/mmHg at max of 300mmHg), and the 9237 is fine up to 25mV/V. However, you should note that the accuracy of the 9237 is only .038mV/V, which means you'll have an accuracy of around +/-8mmHg (38uV/V accuracy/5uV/V/mmHg sensitivity). Be sure this is acceptable for your application.
The excitation from the 9237 should also be fine, as you mentioned, given that the 9237 can excite at 2.5V, 3.3V, or 5V, all within the 0-9V range from your sensor.
In terms of the 8-pin DIN connection, the 9237 won't have a direct hookup for that, so you'll need to use some kind of breakout or transition cable to get the signal though a connector that will work (DB9 or RJ50). If you have to, you should be able to breakout the DIN and exclude that resistor - just wiring the +/-EX and +/- signal into the 9237... but this depends on the device.
So can you use this sensor with a 9237? Maybe, but we can't be sure without a little more information on it. If you can find that information, we can look more closely at getting the sensor to work.
08-03-2012 09:27 AM
Thanks so much for your help and quick response.
Unfortunately, measuring at +/- 8mmHg is not really acceptable for us. Really we are looking for an accuracy around +/- 1 mmHg since we are looking to monitor a system that has a very small margin of error. Is there any solution to this? Would I get better results using an external power source and wiring this into a different module?
Additionally, I do not know whether this is a half, full, or quarter bridge device, but I might be able to find out. The manufacturer's website does not provide much useful information, but here's a link to a distributor that does.
The intended setup is to plug the sensor listed above into an ADLabs bridge amp, and then into one of their Powerlab boxes:
I'm not sure if any of this gives insight into what type of bridge device this is, but that's about all I can offer at this time.
Thanks again! I really appreciate the help.
08-03-2012 05:21 PM
Since you're looking for accuracy within 1mmHg, you'll need something with 5uV/V accuracy. Unfortunately, we do not offer anything with that degree of accuracy for bridge-type measurements - with or without excitation.
One option would be to purchase a different sensor with a different sensitivity - more uV/V/mmHg. 38uV/V or greater sensitivity would work fine with the the 9237, which is our most accurate bridge module. Also, this may be a moot point, but I didn't see any informaiton about the bridge type/configuration in the information you sent me. Thank you for sending it along, though!
Please let us know if you decide to purchase a different sensor, or if you have any other questions on this.