CONTREX CX-1200 - Manual (Page 317)

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Calibrating and Scaling AI1 Together
In some applications you may not know the voltage (or current) to EU/Tm representation, e.g. you may know
that your flow meter operates from 0 to 10 gallons per minute, but you have no idea the voltage produced by
the meter at either end point. You can ‘calibrate’ the signal directly in terms of EU/Tm by setting the
calibration references the same as the scaling references, i.e. set AI1 RA (CP-281) equal to AnlgCal Ref A
(MP-168) for this signal and set AI1 RB (CP-283) equal to Cal Ref B (MP-169) for this signal. These two
points should be discretely different from each other and should be reasonable estimates for the actual voltage
or current range. You would then set the EU@ AI1 RA (CP-282) and EU@ AI1 RB (CP-284) to the
sensor’s operating points used during the calibration process for points A and B respectively.
1. Connect the sensor to the AI1 voltage (or current) pins. Connect pins 3 and 4 together if
using current mode.
2. Set AI1 Mode (CP-280) to “Volts” (1) or “Current” (2).
3. Set Analog Cal Sel (CP-461) to “AI1” (1) to Select AI1 for calibration.
4. Set Analog Cal Ref (CP-462) to “A” (1) to select point A.
NOTE: The old calibration data will be overwritten.
5. Set Analog Cal EN (CP-460) to “On” (1) to start calibration.
6. Run the sensor at the operating point for calibration point A. This is generally your smallest
(or negative) voltage point (or smallest current point). Record the value of this operating
point as sensor operating point A in EU/Tm.
7. Enter an estimate of the voltage (or current) that the sensor is producing at this operating
point into AnalogRef Val (CP-463). Record this value as point A reference voltage (or
current) along side the sensor operating point A.
8. Set Analog Cal Ref (CP-462) to “B” (2) to select point B.
9. Run the sensor at the operating point for calibration point B. This is generally your largest (or
positive) voltage point (or largest current point). Record the value of this operating point as
point B EU/Tm.
10. Enter an estimate of the voltage (or current) that the sensor is producing at this operating
point into AnalogRef Val (CP-463). Record this value as point B reference voltage (or
current) along side the sensor operating point B.
11. Set Analog Cal EN (CP-460) to “Off” (0) to disable further calibration.
12. Go to SCALING/SIGNAL SCALING/P1. Enter voltage (or current) that you recorded as
the point A reference voltage (or current) into AI1 RA (CP-281). Enter the sensor operating
point A (EU/Tm) that the sensor was producing during the point A calibration into EU@AI1
RA (CP-282). This could actually be a time-less unit, but is considered as EU/Tm scaling
because it assumes speed representation for the velocity loop. Enter voltage (or current) that
you recorded as the point B reference voltage (or current) into AI1 RB (CP-283). Enter the
sensor operating point B (EU/Tm) that the sensor was producing during the point B
calibration into EU@AI1 RB (CP-284).
Repeat this procedure for AI2 if necessary. Calibrate AI2 and use the corresponding AI2 parameters.