MAST LABORATORY – LVDT CALIBRATION PROCEDURE
Word Document File for this Procedure: 533578592
Created on: Feb. 12, 07
Author: Jonathan Messier
The following will detail the procedure for calibration of LVDT using the Trimos height gauge and
Calibration VI available on Tough 2.
Procedure assembled by Jonathan Messier on Tuesday, March 08, 2016.
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Power ON!
 Turn on Schaevitz Signal Conditioner at least 15-20 minutes before
calibration.
 If the red LED on the front panel of the conditioner is flashing please
consult the manual.
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Check connections
Plug in Tough 2 (Panasonic Toughbook).
Plug in Trimos height gauge (see Figure 4).
Connect NI- USB data acquisition card to USB port of Tough 2.
Connect communication port (serial connection) of Trimos height
gauge to Tough 2.
Connect the output voltage wires of the signal conditioner to the
NI-.
Figure 1: Signal Conditioner
LVDT attachment
Attach LVDT holder to height gauge base block with four ¼” x 20
screws as shown in Figure 2.
Attach LVDT to LVDT holder with 4 ___ screws.
Attach one end an aluminum extension rod to the core of the LVDT and
the other to the Trimos. An attachment arm with a properly tapped hole
is available for the Trimos, ask a MAST staff-person if this is not
attached to the Trimos already.
Figure 4: LVDT holder
Figure 3: LVDTs
Figure 2: Trimos height gauge
MAST LABORATORY – LVDT CALIBRATION PROCEDURE
Word Document File for this Procedure: 533578592
4.
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Created on: Feb. 12, 07
Author: Jonathan Messier
Load/Setup Calibration VI
CalibrationVI is located on the desktop of Tough 2; double click to begin the program.
CalibrationVI is a National Instruments based software package designed specifically to
interface with MAST lab hardware for quick and easy instrument calibration. A screenshot
of the software is shown in Figure 5.
Figure 5: Calibration software screenshot
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Select the channel to be read by the software from the DAQ channel drop down menu. This
is the channel into which the output voltage wires were inserted when you connected the
signal conditioner to the NI-.
Select the Serial Port to which the Trimos is attached. Typically this will be COM1.
Enter or browse for a directory to save data.
Enter a sensor ID. This label should be an identifier for the specific LVDT and paired
conditioner, i.e. LVDT serial + Conditioner serial. It will make life easier when you need to
recall calibration factors to have an easily readable labeling system for your instruments.
Select LVDT under the Sensor Type drop down menu. This will append your output
filename and take note of the type of instrument in the calibration file.
The Gain switch indicates high or low gain in the calibration file.
MAST LABORATORY – LVDT CALIBRATION PROCEDURE
Word Document File for this Procedure: 533578592
Created on: Feb. 12, 07
Author: Jonathan Messier
Figure 6: Trimos digital display panel.
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Turn on Height Gauge
Press the On/Off button located on the front panel of the Trimos to turn on the height gauge
(see Figure 6).
If the display of the height gauge displays “r.ef”, then raise the arms of the gauge above the
two arrows on the arm track.
Zero Height Gauge
Zeroing the height gauge is not a necessary procedure, however it is recommended to for ease of
interpreting data on the fly. All it does is add an offset to you data in the cal file, but because we
are interested in the slope of a data set, this offset is irrelevant.
 Using the dial of the height gauge move the attached LVDT core into and out of the LVDT
until the voltage reading on the conditioner reads approximately zero.
 Press the Preset button on the height gauge panel. The display should become 0.00000.
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Conditioning the Voltage Signal
Connect a digital volt meter, or NI- USB DAQ to P2 (located on signal conditioner), pins 1
and 2. Pin 1 is DC +, Pin 2 is DC -.
With the LVDT disconnected, unlock the keypad by pressing Fine and Coarse at the same
time.
Press Zero+ and Zero- at the same time. This will cancel zero offsets of the conditioner.
Check the voltage output. If there is a residual error, use the Zero+/– keys to get the error
close to zero (...hundredths of a volt is usually acceptable). The Fine/Coarse keys will
change the step size of the Zero button.
Connect the LVDT to the signal conditioner via P1 (located on conditioner).
Using the height meter, lower the core into the LVDT to a point near the middle of the
measurable stroke. Adjust the position of the rod to get close to zero voltage output from the
conditioner.
Zero the Trimos.
MAST LABORATORY – LVDT CALIBRATION PROCEDURE
Word Document File for this Procedure: 533578592
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Created on: Feb. 12, 07
Author: Jonathan Messier
Move the core rod toward the lead or connector side of the LVDT, roughly half the positive
calibration distance. Make sure your voltage output corresponds to the proper direction, if
not you need to swap the readout cables. Check the readout on the Trimos.
Use the Span+/- to get the half stroke output voltage to 5V.
Press the either the Phase+/- button such that the output voltage increases. Stop pressing
when output begins to decline. Again the Fine/Coarse keys can be used for fine tuning.
Return the core rod to the zero position. Use the Zero+/-keys to get the output close to zero.
Move the core rod exactly to full scale.
Use the Span+/- to adjust the output to +10V.
Move back to zero position and check/adjust output voltage.
Move the rod to full negative stroke. Make sure the output voltage is -10V.
Saving Data
Once a Sensor ID has been entered data can be stored.
Clicking Take Measurement takes a reading from the Trimos and 100 samples from the
DAQ. These mean and standard deviation of the 100 DAQ samples are displayed in Mean V
and Std Deviation, respectively. The Trimos reading is displayed in the Displacement field.
Click Accept Measurements to record the mean, standard deviation, and displacement into
the table on the center of the application.
Click Save to save the table as a .csv file located in:
‘Save Directory’\’Sensor Type_Sensor ID’.cal
The Calibration software will automatically clear all fields and your data will be saved.
Suggestions!
Take plenty of data! MAST recommends taking a data point for every +/-20% of full range.
For example: If we had a 3 inch (full scale) LVDT, we would take position and voltage data
for ±2V, ±4V, ±6V, ±8V, and ±10V (10 data points) which would correspond to
displacements of ±.3”, ±.60”, ±.90”, ±1.2”, ±1.5”, respectively.
The calibration factor found in the .cal file is calculated as the linear fit of the data points in
the data file. Use this calibration in the HCC when taking data on the DAQ.
Do not separate an LVDT from its signal conditioner are calibration. The change in
voltage/resistance in the connection between the sensor and conditioner plays a significant
role in the voltage output; any changes to this connection will alter calibration.
Label your calibration file such that it reflects the combination of LVDT and signal
conditioner used, for example:
Sensor ID: 123_4_567
Where 123 indicates LVDT number, 4 is the stroke length and 567 is the signal conditioner
number.