Need a bridge amplifier for my transducer

[abdel2]

I have a pressure pad which outputs very low voltage (uV-mV). When I try to record signal from it in the presence of other channels, I see a lot of cross-talking. Is there any good bridge amplifier that I can use (one with low output impedence aswell)? Something like this one (but with BNC input/output):

 http://www.wpiinc.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=46&category...

All the amplifiers that I have come across so far only work with transducers specifically created by the respective company.

[Henrik_Volkers]

What Type of transducer do you have?  Full,half,quarter bridge? Needed uncertainty?

Bridge-Amplifier I know don't work with BNC input, since the bridge also need a supply voltage.

My personal favorite for bridge amplifier is HBM (I used the MVD2555 in a Lab version), however of course you also get DAQ with bridge amplifier from NI.

[abdel2]

I am not sure about the exact configuration. Here is its description:

"The MLT1132 Piezo Respiratory Belt Transducer generates
a voltage when there is a change in thoracic or abdominal
circumference due to respiration. It contains a piezoelectric
device that responds linearly to changes in length.
The transducer is a solid-state device that requires no
excitation and connects directly to a PowerLab BNC input.
It is comfortable to wear, rugged and reliable. "

http://www.adinstruments.com/products/hardware/research/product/MLT1133/

I'll look at HBM. Thanks!

By BNC, I meant, the input should be BNC (because the tranducer has a BNC connection). The amplifier itself can have a separate connection for power. Do you think something that costs a bit less will also work (I'm guessing HBM is at least over a grand)?

Message Edited by abdel2 on 06-17-2009 11:51 AM

[Henrik_Volkers]

I was miss leaded by your words bridge amplifier and pressure transducer. I assumed a pressure transducer with a (resistive) bridge, which is a very common type.

However .....

You don't need a bridge amplifier.  Depending on your acquisition hardware you maybe don't even need an ordinary amplifier.  

What acquisition hardware do you have?  Input range and input impedance? Setup?  Maybe it's possible to avoid the crosstalking.  

VERY IMPORTANT:

If you deal with electronics near human bodies, make sure they apply the according safety rules! This might be OK with your current setup, but will(might) be void if you use an ordinary amplifier not valid for 'medical' use. 

Message Edited by Henrik Volkers on 06-19-2009 01:22 PM

[abdel2]

I am using a PCI 6221 DAQ card with 2090A BNC panel. Eventually we might replace the PCI board with a USB one (same model - 6221). I had set the input range to -0.1/+0.1 volts, but now that I rechecked the manual, I can only go down to -2/+2. I wasn't getting any errors but maybe the card was defaulting to -10/10 and that's why I wasn't getting a good reading.

I am not quite sure about the tranducer's output resistance. On the data sheet it says the device resistance is 10^8 so maybe that's it. This seems very high and is probably the cause of crosstalk as some NI articles suggest (high tranducer output resistance = ghosting). The output range of the tranducer is 20 mV to 400 mV. That's why I was also looking for an amplifier that had very low output resistance.

[Henrik_Volkers]

The manual for the 6221 tell me +- 0.2V and 10GOhm input impedance. Crosstalk is named to be -75dB.Should be fine....

I couldn't find the 2090 BNC panel. Is it the same like page 17 here?

Can you use/try differential inputs (FS)? If yes try an additional/separate  analog grounding while using.  

Do you connect the sensor directly to the BNC board? 

Do you get good readings while using only this one sensor (the rest disconnected)?