CONTREX CX-1200 - Manual (Page 120)

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AUX ANALOG SIGNALS
The Aux Analog Signals screens consist of the Input 1 screen, the Input 2 screen and the Output screen.
Input 1
The Auxiliary Analog Input 1 signal (AI1) can be used as a sensor offset to the Lead signal in Lead plus
Offset applications, sensor offset to the Follower signal in Follower plus Offset applications or as the Phase
signal in the Non-Sync Feedback + Phase. This is selectable through LdOfstSource (CP-207), FbOfstSource
(CP-208) and Phase Source (CP-356).
Go to the Scaling/Aux Analog Input 1 screen. AI1 RA (CP-281), EU@AI1 RA (CP-282), AI1 RB (CP-283)
and EU@AI1 RB (CP-284) scale the Auxiliary Analog Input 1 signal from volts or milliamps to EU.
To scale the Auxiliary Analog Input 1 signal in terms of EU, you must first determine the Engineering Units
that are relevant to your application and determine how this signal is used. If used as an offset in offset
applications, this signal is typically scaled to the same EU representation as the chosen Feedback. For
example, your EU ‘speed’ representation for this signal may be in RPM, feet/minute, inches/second, or pages
per second.
Once you determine the EU representation for this signal, you need to scale the input voltage (or current) by
means of a linear two point method. Typically, the two points (A and B) are chosen as the endpoints of the
range of operation - the minimum and maximum voltage (or current) and the minimum and maximum EU.
The two points also determine the ‘polarity’ of the signal by defining either a positive or negative slope.
Enter a reference voltage (or current) for point A into AI1 RA (CP-281). Enter the EU that corresponds to
this voltage (or current) into EU@AI1 RA (CP-282). Enter a different reference voltage (or current) for
point B into AI1 RB (CP-283) and the corresponding EU into EU@AI1 RB (CP-284).
For example, a pot might be used to add the sensor offset to a lead frequency. Your Lead is scaled for Feet/
min. The supply voltage on the pot is +10 volts. You want the midpoint (5 volts) to represent “0” EU (Feet/
min). A voltage measurement of 10 volts needs to increase the speed by 100 Feet/min and a voltage
measurement of “0” volts needs to decrease the speed by 100 Feet/min. Enter “0” into AI1 RA (CP-281)
and -100 into EU@AI1 RA (CP-282). Enter 10 into AI1 RB (CP-283) and 100 into EU@AI1 RB (CP-284).
AI1 Mode (CP-280) should be set to volts (1).
The scaled range of the Analog Input 1 signal (e.g., 0 to 10 volts) should be similar to that at which the input
was calibrated. Go to the Device Tests/Aux Analog Tests/P3 screen and select the signal with Analog Cal
Sel (CP-461). Do not enable calibration. The two points for calibration should be displayed at the bottom of
this screen in AnlgCal Ref A (MP-168) and AnlgCal Ref B (MP-169). Verify that the calibration range is the
same range as the operating range. If not, recalibrate the input signal. Refer to Drive Setup-Calibration:
Calibration for additional details.
There may be instances where you do know the voltage (or current) to EU representation, but you have no
idea the voltage produced by the sensor at either end point. You can ‘calibrate’ the signal directly in terms of
EU 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 AnlgCal 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. Now you can perform the calibration procedure with the
sensor connected to this input. Enter you estimates for AI1 RA and AI1 RB into AnalogRef Val (CP-463)
for the two points of operation/calibration. Enter the EU corresponding to these two points into EU@AI1 RA
and EU@AI1 RB after the calibration is completed. Refer Drive Setup/Calibration: Calibration for
additional details. For the formulas for the Auxiliary Analog Input 1 calculations, refer to Appendices:
Appendix B.