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I'm using a Spectramed/Statham P23XL pressure transducer with a Gould (13-6615-50) signal conditioner. I can get 0-2.5V out the back of the SC to map to 0-100mmHg, but outputs below 20mmHg are inaccurate/near zero. How do I get these lower level readings; or do I need to account for some non-linearity - if so how?
You'll have to refer to the specification sheet for your device to determine that. They may have a characteristic curve for your device. If you determine that it is non-linear, you'll have to make your own V-to-mmHg conversion. If they supply a formual, you are in luck. If not, then you may have to develope a table for the values in the non-linear range.
The performance that you see is fairly typical of many types of pressure transducers. The deflection of the metal diaphram can not be made to be exactly linear across the entire range of operation. The manufacturer will typically specify a single slope that has been determined at the full scale output level. It is a sound practice to try to limit the use of a transducer to the 40-80% range to avoid the necessity of a complicated calibration procedure. If you wish to use the entire range of the sensor, you will need to perform a detailed ( 4th or 5th) order calibration with an emphasis on the lower 20% of the pressure range.
