How to Calibrate the SC-200 LVDT Signal Conditioner

How to calibrate the Alliance Sensors Group SC-200 LVDT Signal Conditioner

 

To perform this task, you will need the following tools and materials:

  • A 24V DC power supply
  • A DC volt meter
  • An SC-200 LVDT Signal Conditioner
  • An LVDT test fixture with digital micrometer
  • An AC LVDT
  • Small Screw Driver

Before proceeding, factory default settings are adequate for most standard industrial LVDTs and no adjustments are typically required. In the event that the LVDT requires different settings from the factory defaults you will need to adjust the SC-200 to match to your particular LVDT requirements. To perform these adjustments, the DIP switches can be accessed by pushing in the tabs on both the top and bottom sides of the case with a small screw driver, then sliding out the board to access the electronics. Please consult the label on the case or the Quick Start Guide instructions for proper DIP switch position and jumper settings for RS 485 addressing, excitation frequencies, voltages, analog output settings and filtering.

After the internal DIP switches have been set, begin by connecting the power supply. Connect the positive side of the power supply to terminal 4 of the red J4 terminal block and the negative side of the power supply to terminal 3.

Next connect the digital voltmeter, which will measure the output from the SC-200. Connect the positive side of the voltmeter to terminal 4 of the J3 green terminal block and the negative side of the voltmeter to terminal 3.

When connecting the LVDT, attach the primary high of the LVDT to terminal 1 of the J1 black terminal block and the primary low to terminal 2.

Connect the secondary low of the LVDT to terminal 3 of the J1 black terminal block and attach the secondary high to terminal 4.

Both secondary center tap wires must be connected together and can be attached to terminal 1 of the J2 blue terminal block for convenience.

For this demonstration we’ll be using an AC LVDT with a plus and minus 0.25" measuring range or 0 to 0.5" total stroke and the SC-200 analog output setting at 0 to 10 VDC output.

 

Now, with all the connections made and the LVDT positioned into the test fixture we will apply 24 VDC power to the SC-200.  The red Power LED on the face of the unit will illuminate indicating power is present. The green “P” LED will illuminate as well, indicating that the SC-200 is operating as a master.  It is important to allow 15 minutes time to fully warm up before proceeding with the calibration.

With the SC-200 fully warmed up, we are ready to place the SC-200 into calibration mode. This is accomplished by depressing the “Full Scale” and “Zero” buttons simultaneously until the power LED begins to blink, indicating we have successfully entered the calibration mode.

Using the micrometer, adjust the LVDT until the SC-200’s zero indicator LED glows solid. This is the null point of the LVDT meaning that the core is at its center stroke. We now reset the digital micrometer readout to zero.

Next, using the digital micrometer, displace the LVDT by minus 0.25 inches. This will take us to the negative end, or zero inch position of the LVDT’s stroke range, and will be the SC-200’s 0 VDC output position. Enter the zero point position into the SC-200 by momentarily holding the “Zero” button until the positive indicator blinks once. The negative indicator will now glow solid and the positive indicator will begin to blink. This shows that we have successfully set the zero point position.

We now reset the digital micrometer readout to zero.

Next, we displace the LVDT by plus 0.5 inches. This will take us to the positive end, or 0.5 inch position of the LVDT’s stroke range, and will be the SC-200’s 10 VDC output position.  When the position has been reached momentarily hold the “Full Scale” button until both the positive and negative indicators illuminate solid. This indicates that the calibration has been successfully completed.

Finally, to return the SC-200 to Operation Mode, depress both the “Full Scale” and “Zero” buttons until the power indicator glows solid. The device is now ready for Operation.

We now observe that, as displayed on the DC voltmeter, that the output voltage from the SC-200 is 0 VDC with the LVDT at the zero position and +10 VDC with the LVDT at the 0.5 inch position.