Part Number:INA129
Hi,
Marek Lis addressed an earlier question for an application. I have since performed some circuit modeling with tina-ti. I have a need to measure a dynamic pressure variation in a pressure chamber that last for a couple of milliseconds. I would do this using a wheatstone bridge and a strain gauge. Many of the references on this topic pertains to weight measurements which have fairly low bandwidth requirements and differential signals perhaps in the milli-volt range. For me, my bandwidth requirement is about 4 khz and signals in the tens of micro-volt range. So I am concerned about noise and drift. My modeling includes a simulated strain gauge resistance controlled by a voltage waveform, an ina129, opa333, a reference source and regulator. I have attached a number of files from my modeling effort. From what I have seen, a simple network of capacitors and resistors are used to provide a low pass filter on the input of the instrumentation amplifier noise immunity in weight sensing applications. Considering that my bandwidth is quite large and the gain that I am using, the natural roll off of the amp is providing this filtering component. Is there anything else I can do? I have put in some bypass capacitors to assist in noise immunity too. Would leaving the non-trace copper on the top/bottom of the pcb assist in noise immunity?
I have attached the circuit design and results (gain, transient and noise). The noise modeling performed is not complete since I believe that the lp38798 macro does not include noise contributions. Perhaps the ref5020 does not either. Do you have any comments/suggestions on other noise immunity and drift minimizing techniques that I could/should employ? I have not modeled and esr considerations either.
Thanks.
Al
