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1. 05:46 PM - Instrumentation amplifiers (Finn Lassen)
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| Subject: | Instrumentation amplifiers |
Trying to measure pressure in front of my radiators to somehow get
uniform airflow through entire rad surface.
A few years ago I bought 5 MPX10DP 10kPa (1.45psi) pressure sensors
because they were relatively inexpensive.
Been measuring 1" from each corner and center. But have now added
steering vanes in # pattern -- in other words rad surface now divided
into 9 squares.
Throwing good money after bad I just ordered additional 4 MPX10DPs.
Problem with the MPX10 sensors is they are not amplified (nor
temperature compensated). Only outputs 35mV/10kPa. However outputs are
offset at about 2.5V when fed 5V. Basically wheatstone bridge.
The smarter move would have been using MPX5010DP sensors. They are
internally amplified and temperature compensated. Output between 0.5 and
4.5V. However they are considerably more expensive.
I've been using two of LM324 opamps for each sensor to handle offset and
get the amplification I'd like. Had not looked at temperature
compensation because mainly interested in relative pressures over the 5
channels.
Not expecting to see more than 20 inH2O or 5 kPa so 250x amplification
would be ideal but at least 140x to get full range from the MPX10DPs.
Now I've seen mention of INA122 (about $5+ each) and similar
instrumentation amplifiers which are designed for the MPX10DP type of
sensors. Came across the INA350CDS instrument amplifier reasonably
priced at less than $1 at Mouser. However only 50x amplification.
Thinking of making a PCB for the 9 MPX10DPs and amps.
Before I do I'm wondering if any of you have experience in this area
(differential input instrument amplifiers with output going to 0-5V
input A/D converters) and may have other suggestions. Inexpensive
differential input instrument amplifiers with digital outputs? Or some
other modern ICs I'm not aware of.
Finn
P.S. I did consider 3D printing a 9 to 1 valve to be driven by a stepper
motor and just one MPX5010DP pressure sensor but worried about how long
it would take for pressure to settle out after changing from one input
to the next. Currently logging the 5 channels 2 times per second but
able to log much faster.
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