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Displacement Calibration Apparatus

Instrument cover photo.

This documentation covers part number 10-0000027

Overview

The displacement calibration rig makes it easy to accurately calibrate lineartransducers with a total range of up to two inches. With proper setup it allows for repeatable calibration in just a few minutes. The calibration software automatically creates the calibration curve and a data file with every calibration point.

Setup

The displacement calibration rig is a sensitive instrument that requires alignment after shipping and periodically before use. The tools required to calibrate the device are included with the kit.

Alignment Process

The alignment process of the displacement apparatus involves aligning the digital indicator on the base to be exactly perpendicular to the stage. Without correct alignment, calibration of the DCDTs will not be accurate due to cosine error. Typically misalignment showing greater than 0.002” will need to be corrected.

Tools Needed:
0.5” and 1.0” Gauge Blocks
 1.27mm Hex Key

  1. Adjust the stage so that it is a small amount behind center using the adjustment screw, then zero the readout on the digital indicator.

  2. Gently pull back the quill and place the 0.5” gauge block as shown. Make sure the surfaces of the block are clean.

    Setting Gauge Block.

  3. Note the measurement shown on the readout. In the image above the block is measuring at 0.501”, which is higher than its actual width.

  4. Repeat steps 2 and 3 with the 1” gauge block. If the readings are different than expected alignment is necessary. Typically the alignment is acceptable if the error is roughly 0.001”, and alignment is necessary if it is greater than 0.005”.

  5. For minor misalignments (<0.003”) often the quill at the top of the indicator can be tapped gently to realign it. If this doesn’t work further alignment is necessary. This can be accomplished by slightly loosening the screws on the bottom of the plate that hold the indicator with a hex key and gently rotating it. This is usually made easier by leaving one screw tight, and barely loosening the others.

    Realignment

  6. Checking alignment involves repeating steps 1-4 of the process each time the alignment is changed. The goal of the alignment is to have each gauge block measure as their calibrated length on the indicator. (0.5” block measures as 0.5000”, and 1.0” block as 1.0000”) but an error of ±0.002” is typically acceptable.

  7. Once the correct alignment is achieved the screws can be tightened. After tightening the screws, check the alignment again to make sure it hasn’t moved.

DCDT Calibration

A video of this process is available on our website or here.

  1. Place the DCDT in the holder so that a small amount of the DCDT is protruding from the front. (This can vary depending on the model.) Then gently tighten the thumbscrews on top to hold it in place.

    Inserting DCDT

  2. Take the included core nuts and install them onto the DCDT core. The larger nut should be installed onto the core with the flange facing backwards. The core can then be put through the hole in the core plate on the slider. Screw on the second nut loosely so that the core can still move.

    Installing DCDT Core

  3. Move the carriage so that the core slides into the DCDT. Once inserted the core nuts can be tightened. This ensures the core is properly aligned.

    Inserting DCDT Core

  4. Using the adjustment screw, move the stage so that it is centered on its base and the edges are flush. Zero the indicator by pressing the zero button.

    Zeroing the Device

  5. Apply power to the transducer and connect it to the computer via your data acquisition system.

  6. Using the calibration software, name the transducer and specify the units it will be calibrated in. (The supplied unit displays in inches, so this will be the unit)

    Transducer Setup

  7. Select the input channel that the transducer is on by selecting browse in the input channel menu.

    Select the input channel

  8. Select the sampling rate of the system. If the system is capable of 10,0000 samples/second this is best, but lower sampling rates will also work. Next, select the seconds to average. One second is typically acceptable, but in systems with significant noise higher averaging times may be beneficial.

  9. Once all sampling parameters have been set, select start in the calibration menu. Move the transducer core on the carriage until the voltage displayed on the screen is close to zero (±100mv), then secure the carriage by tightening the knob on its side. This centers the core in the transducer.

  10. Begin calibration by adjusting the stage until the indicator reads near one of the extremes of the transducer range. (For a 1” transducer this will be ± 0.5”) This instrument is capable of calibrating transducers with a total range up to 2”.

  11. To begin recording, keep the mouse cursor in the “Calibration Points” box on the screen and press the button on the cable connecting the indicator to the computer. This should cause a point to appear on the graph.

    Begin Recording
    To complete the calibration curve, rotate the adjustment screw on the stage a couple of turns in the desired direction and press the button to record again.Repeat this process until the entire range of the transducer has been recorded. This will create the calibration curve. Moving the same displacement with each measurement isn’t necessary because the displacement is precisely recorded by the digital indicator. Complete the calibration by repeating the process in reverse to fill out the plot.
    Complete Calibration Curve

  12. When the calibration curve is complete, select the complete button in the calibration menu, then click save and choose the save location of the file. You can then open the calibration file using notepad. This will display the parameters of the calibration, and the calibration points.
    Complete Calibration Curve

Revision History

Date Changes
September 2024 Initial Release