Bench Testing a 35xx Series Pressure Sensor with a Ratiometric Output


  • This Bench test applies only to sensors with a Ratiometric output. 
  • This is indicated by the T in the part #, highlighted below in yellow:


When you are troubleshooting an issue with your sensor or device, we strongly recommend completely removing it from your system to bench test it.  Many times, the customer’s wiring/PLC/controller can incorrectly influence the testing circuit and adds variables to your testing.  The method below reduces as many variables as possible to allow you to Bench Test your sensor and ensure it is working OK.  If there is an error in the wiring or controllers, this will attempt to remove them from the equation.


1.    Preparation:
      a.    Remove the sensor from your system completely.
                 i.   If that is not possible, then only electrically remove it from your system.
      b.    Make sure your power supply and multimeter are off.
      c.    Download the 3500 Series bulletin here for reference: 
      d.    Reference the pinout chart for the three pins/wires used in the voltage output:



2.    Basic wiring diagram: 
       See below.


3.    Components for the Bench Test:
      a.    Known good Power Supply, capable of producing 5.0 VDC. 
                    i.   It is very important to have exactly 5.0 VDC.
                   ii.   See write up on Ratiometric sensors here:  MKTG - PLEASE PUT LINK TO RATIOMETRIC BLOG HERE
      b.    Known good Multimeter, set to measure DC Volts (READOUT).
      c.    Appropriate mating electrical connectors or jumpers (if needed).

4.    Wiring your Bench Test Setup:
      a.    From your Power Supply, connect a wire from the (+/RED) connection to the VSUPPLY input on your sensor.
      b.    From the (-/BLACK) connection of your Power Supply, connect a wire to the Ground/Common
              connection of your sensor.
      c.    Also from the (-/BLACK) connection of your Power Supply, connect a wire to the (-/BLACK) connection
             of your handheld Voltmeter (READOUT).
      d.    From the (+/RED) side of your Voltmeter, connect a wire to the Vout connection of the sensor.
      e.    Do not connect anything to the other unused wires/pins of your sensor.

5.    Gotcha’s:

      a.    Make sure you have NOTHING else connected to this circuit.  This will eliminate any variables in the test.
      b.    Make sure your Multimeter is set to VOLTS.  Not Amps or Ohms.
      c.    Make sure your probes are in the correct holes of the Multimeter to read VOLTS or VOLTAGE. 
             Some meters have one connection for amps and one connection for volts/ohms.
      d.    If you meter is not Auto-ranging, then set it to read in the 0 thru 5 or 0 thru 10 VDC range.
      e.    If you are using a mating connector, pay attention to the Pin callouts.  They are opposite on the sensor
             versus the harness so when you connect them, they line up correctly.
                         i.   For example, the Packard pinouts:

You can see the A and B pins are opposite in the two pictures. 

6.    You are now ready to start the BASIC Bench Test:
        This will give you a simple health check of the sensor to make sure it has an output.
      a.    Double check all wiring.
      b.    Turn on the Multimeter, set to the Voltage range.
      c.    Turn on your Power Supply.  As per above, set it to exactly 5.0 VDC.
      d.    With no pressure on the sensing port of the sensor, you should see 0.5 VDC (or 500 mV DC)
             plus or minus a small error Zero Tolerance error. 
             The Zero Tolerance error spec for the 3500 is 0.5% of Span. 
             Span is 4VDC (4.5V less 0.5V).
      e.    If you see any output that is greater than 0.52 VDC or less than 0.48 VDC, you might have a bad sensor.              
             If it is in that range, then you are OK.
      f.    Turn off the Power Supply and Multimeter.

7.    If you have a pressure source available, you can perform the ADVANCED Bench Test:
       This will allow you to check the sensor at pressure. 
      a.    Connect to a known reliable and accurate pressure source. 
             Be careful when high pressure is involved.
      b.    Turn on the Multimeter.
      c.    Turn on your Power Supply, set it to 5.0 VDC.
      d.    Repeats Step 6 above:  With no pressure on the sensing port of the sensor, record the Voltmeter reading. 
             This is your Zero Point value.
      e.    Apply the appropriate maximum measuring pressure for your sensor.  This will be labeled as RANGE
             on the sensor.  Note the value on your Voltmeter and record it.  This is your Max Point Value.
      f.    To calculate if the sensor is operating correctly, use this formula:
                    i.   Max Point Value minus Zero Point Value = Span Value

                         Max Point Value minus Zero Point Value = Span Value
                         4.49 VDC – 0.51 VDC = 3.98 V span

                         Zero Point = is OK for 0.51VDC is within the allowable range of 0.5% of Span
                         Ideal Span is 4.0 VDC, 0.5% of 4.0 VDC is 0.02 VDC
                         So, range of Zero Value is 0.48 thru 0.52 VDC

                         Span Value = is OK for 3.98 VDC is within the allowable range of 0.5% of Span
                         Ideal Span is 4.0 VDC, 0.5% of 4.0 VDC is 0.02 VDC
                         So, range of Span Value is 4.49 thru 4.53 VDC
                                  (taking into consideration that your span started at the Zero Point Value of
                                  0.51 VDC, and not at 0.5 VDC)

      g.    Turn off the Power Supply and Multimeter and disconnect all your wiring.

8.    If you find that your sensor is not reading correctly, contact Gems with your part #, PO #,
       findings and for next step options.