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Pressure Sensors (App Note)

This application note is about selecting and using pressure sensors.  Most pressure sensors are constructed as a bridge of strain gages or similar elements, and some then also have built-in signal conditioning.

Power Supply:  The ideal sensor runs off 5 volts DC so you can power it from the LabJack, but if a sensor needs 12 or 24 volts DC that is easy to provide with an external power supply.

Signal:  The ideal signal is a voltage signal that matches the analog input range of the LabJack.  With the ±10 volt inputs found on most LabJacks, the typical signal ranges of 0.5-4.5, 0-5, 0-10, or ±10 volts are all excellent options.

Ratiometric Signal:  Many sensors provide a ratiometric signal, meaning that if the power supply changes +3% (for example) the output signal will also change +3%.  In particular, all raw bridge signals are ratiometric and most 0.5-4.5 volt amplified signals are also ratiometric.  The 5 volt VS source from the LabJack is typically regulated to ±5%.  One primary strategy to improve accuracy with ratiometric signals is to use another analog input to measure the actual value of the supply voltage whenever you acquire a signal reading.  The other general strategy is to use a supply voltage that is more stable and lower noise, and a couple options for that are a DAC output from the LabJack or the LJTick-Vref.

Raw Bridge

If the output is specified as something like 2 mV/V, that is a raw bridge sensor.  Another thing to look for is 4 wires labeled something like Excitation+, Excitation-, Signal+ and Signal-.  A raw bridge sensor can be handled, but is certainly more demanding than a signal-conditioned sensor.  For more information see classic forum topic #4376, especially post #13.

Signal-Conditioned

These generally have 3 wires:  Vsupply, Ground, and Signal.  The signal is an easy-to-handle high-level voltage output such as 0.5-4.5, 0-5, 0-10, or ±10 volts.  You will also find 4-20 mA current output versions that have 2 or 3 wires.

Some sensors provide 4-20 mA current signals.  These are pretty easy to handle as discussed in the 4-20 mA App Note, especially with the LJTick-CurrentShunt, but they almost always require an external power supply.

NXP (aka Freescale) is a good source for pressure sensors.  Look for sensors they call "Integrated":

Digikey sells lots of sensors from NXP and other manufacturers.

Omega is another sources that sells lots of sensors from various manufacturers.