Kaman KDM-8200 - Manual (Page 30)

30
Kaman Precision Products
Calibration
Full Scale
Full scale calibration produces an output voltage that varies from 0 Vdc when the target is
Calibration closest to the sensor (plus offset) to some maximum positive voltage when the target is farthest
Procedure from the sensor.
DISPLACEMENT
offset
VDC
0
Full Scale Calibration
1. Install the sensor in the calibration or application fixture, ensuring that when the target
is at its closest point to the sensor, there is a gap (offset). With curved targets, decreasing
offset will improve linearity; for flat targets, increasing offset slightly will improve
linearity. In either case, never allow the target to strike the sensor face.
2a. Position the target using the micrometer fixture or spacers so that the total distance
between the sensor and target is equal to the specified full-scale displacement for that
sensor, plus offset. See the Sensor Specification Table in Part 3: EQUIPMENT for
standard offsets.
2b. To calibrate for a specific sensitivity, follow the procedures in Step 2a, then adjust the
Gain control so that system output equals your desired new full-scale output voltage.
3. Position the target to zero displacement (plus offset). Adjust the Zero control until the
output voltage reads 0 Vdc.
4. Position the target at mid-scale plus offset and adjust the Gain control until the output
voltage reads the desired mid-scale value. For example, assuming 10mV/mil sensitivity,
and your full-scale voltage is 1 Vdc at 100 mils, then the system output at mid-scale
should read 0.5 Vdc at 50 mils.
5. Reposition the target at full-scale displacement, plus offset. Read the output voltage and
note the difference between the actual reading and the desired reading. Adjust the
Linearity control (Coarse, then Fine) until the output reads the desired voltage level, then
continue past the desired reading by an amount equal to the first difference you noted.
This technique is called 100% oversetting and is used to reduce the number of iterations
needed to calibrate the system. For example, if the output reads 1.350 volts and the
desired reading is 1.000, adjust the Linearity control until the output reads .650, or 1.000-
.350. If the output reads .800, adjust linearity until system output reads 1.200, or 1.00 +
.200.
6. Repeat Steps 3 through 5 as many times as necessary until the desired output voltage at
each point is reached. No further adjustment of the Zero, Gain and Linearity controls
will be needed when proper calibration is obtained.