Making pressure measurements, and storing pressure data for review and analysis is an extremely common and important data acquisition application. Whether it’s water pressure at your local utility, or air pressure in an industrial compressed-air system, pressure data can be an invaluable resource, helping maintenance technicians and managers make informed decisions.
In this application note, we’ll demonstrate the ease with which pressure data can be displayed, archived and analyzed using DATAQ Instruments model DI-2108-P, WinDaq data acquisition software and an off-the-shelf 0-100 psi pressure sensor.
Almost any Dataq device can be used for this measurement but we chose the DI-2108-P because of its 16-bit resolution and uni-polar measurement ranges. The uni-polar ranges make the instrument ideally suited for sensors and/or transducers with outputs that never drop below zero. This is because the 16-bit resolution of the device is spread out over a more narrow range (0-5 or 0-10V, as opposed to ±5 or ±10V), effectively doubling the measurement resolution. For more on ADC resolution please see the article How Much ADC Resolution Do You Really Need?
The pressure sensor we’re using requires an excitation (supply) voltage, and has a 0.5 – 4.5Vdc output signal that is directly proportional to pressure.
We’ll begin by connecting the sensor to the DI-2108-P. The pressure sensor has three connections; an output, excitation (supply) and common/ground connection. We’ll connect the output to the positive (+) terminal on one of the analog inputs, the suppy connection to the +5V pin and the ground connection to the GnD pin.
Setup and Scaling
Scale WinDaq to display pressure (psi) instead of volts. Choose ‘Engineering Unit Settings’ from the ‘Edit’ pull-down menu. Enter 4.5 for Upper Level > Volts and 100 for Upper Level > EU. For Lower Level > Volts enter 0.5 and for Lower Level > EU, enter 0. You can enter psi for EU Tag.
Because the sensor ouput is linear, a change in pressure will result in a directly-proportional change in the voltage signal acquired by the DI-2108-P. So as pressure rises to 20 psi (20% of the full scales range of the sensor), the output signal will rise to 1V (20% of the full-scale voltage output).
In our example, pressure will never drop below 0 psi, nor will it rise above 50 psi, so we will choose ‘Limits’ from the ‘Scaling’ pull-down menu and enter ’50’ for as the Top Limit, and ‘0’ as the Bottom Limit
With WinDaq scaled to display pressure in psi, applying pressure to the sensor yields a curve, showing pressure rise and fall with respect to time.
Featuring 0-5V and 0-10V unipolar measurement ranges, the DI-2108-P is well suited for pre-amplified sensors with 0-5V, 0-10V or 4-20mA (using a 250 ohm shunt) analog outputs.
While the DI-2108-P, with it’s unipolar ranges, is an ideal solution for this application, there are a number of other DATAQ data acquisitoin products that are up to the task. Similar products with programmable bipolar measurement ranges, like the DI-2108, DI-4108, or DI-4208 series loggers, or signal-conditioned solutions like the DI-4718B or DI-788 with DI-8B41-02 analog voltage modules would work well, albeit, with half the resolution.
This application note demonstrates the ease with which physical properties such as pressure, rpm, acceleration, etc. can be digitized, displayed and recorded for analysis using DATAQ Instruments data acquisition products like the DI-2108-P and accompanying WinDaq data acquisition software.