Pressure Sensors (App Note)

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

Ideal Sensor Requirements

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. See our Externally Powered Signals App Note for power supply recommendations and related information.

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.

Pressure Sensor Types

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 the Bridge Circuits App Note.

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.