For my senior design project, we have various sensors (Thermocouples, Heat flux sensors, load cell) plugged into our DAQ. We are using LabView and some National Instruments devices (ugh) and discovering that our loaned equipment doesn't have the resolution necessary to read accurate values from our heat flux and load cell sensors. The DAQ can read around a 100 mV range effectively. The heat flux sensor provides values in the microvolt range (0-100uV IIRC) and the load cell is in the milivolt range (0-5mV). We're looking into getting a better DAQ, but I was wondering if there is a way to easily amplify these signals into the volt range? Our grad student we have working for us is very concerned about impedance and other factors that can throw off our readings and is very against any sort of amplification circuits. Is amplification a viable route, and how would we go about amplifying the signal?
1 Answer
Your DAQ probably looks pretty similar to an opamp from the sensors perspective. I can't imagine your DAQ having anything overly special about its input impedance. Even if it did, you would need to be concerned about the input impedance of a new DAQ.
What I would be concerned about is the noise floor associated with your sensors and circuitry. You are needing to look at voltage ranges that most oscopes can't even see. You will need to put time into every aspect of your signal acquisition including board layout and shielding from noise.
You may be able to to use just a simple op-amp to provide your gain, but be cautious of the noise as opamps can be very noisy if you aren't careful on what you buy. There are other methods of providing a gain, but I suspect that will all have issues with noise.
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\$\begingroup\$ This may not be true. When you read a thermocouple it is very important that the first device to amplify it's reading is designed for it. Small PCB trace missmatch can cause resistance changes which result in many errors. \$\endgroup\$– KortukCommented Nov 5, 2010 at 1:00
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\$\begingroup\$ In our case we don't need to worry about the thermocouples, we have a separate device reading those values, but this is good to know. \$\endgroup\$– MGSotoCommented Nov 5, 2010 at 1:12
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1\$\begingroup\$ Then +1 on the answer. I would suggest you use op-amps to give gain. I would suggest that you take time to research this. The point of senior design is to learn these methods. If i give you the answer I will be shorting you the learning process of finding application notes online. I think nothing could be better than you coming back and posting an answer explaining how to do this in detail with application notes and simulation. \$\endgroup\$– KortukCommented Nov 5, 2010 at 1:58
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\$\begingroup\$ I completely agree. While I'm more in the software side of things, I definitely have a part in the electric portion of it as well. I came here not so much for a direct answer, but guidance because I wasn't sure who to trust for information. \$\endgroup\$– MGSotoCommented Nov 5, 2010 at 4:02
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\$\begingroup\$ @MGSoto from my experience when I had my Senior Design project, don't always trust grad students. Look at what the students specialization is and decide if that specialization would give him the ability to know what he is talking about on that subject. On the other hand, if he has any part in your grade, you should try to make him happy. \$\endgroup\$– KellenjbCommented Nov 5, 2010 at 5:08