| ??? 07/19/07 23:17 Read: times |
#142056 - Consider Responding to: ???'s previous message |
...a semiconductor bridge pressure sensor. They have a very non-zero output at zero pressure (upto about 35mV) . Also, they have a terrible co-efficient of output with temperature (1200ppm/deg C !)
Anyway, apply a gain suitable for the range you require - (0-5 V out = 0..1 PSI (1/14 Bar)) a calculated gain of say 400 in my case, involves multiplying the initial zero by 400 - which means the system saturates on zero load. Full output under load is only 20mV ! The current (no pun intended) system uses a Burr-Brown instrument amp, with another amplifier creating an offset based on the bridge excitation signal. <http://www.alliedelec.com/Images/Pr...30058.pdf> The T/C problem is corrected very neatly with an LM334 constant current source, and a "leak" resistor around it feeding the bridge. The system is accurate to 1% -ish over 0-90 C. Steve |
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