CONTREX CX-1200 - Manual (Page 121)

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Input 2
The Auxiliary Analog Input 2 signal (AI2) can be used as a offset to the Lead signal in Lead plus Offset
applications, 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 2 screen. AI2 RA (CP-286), EU@AI2 RA (CP-287), AI2 RB (CP-288)
and EU@AI2 RB (CP-289) scale the Auxiliary Analog Input 2 signal from volts or milliamps to EU
To scale the Auxiliary Analog Input 2 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 AI2 RA (CP-286). Enter the EU that corresponds to this
voltage (or current) into EU@AI2 RA (CP-287). Enter a different reference voltage (or current) for point B
into AI2 RB (CP-288) and the corresponding EU into EU@AI2 RB (CP-289).
For example, a pot might be used to add an 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 AI2 RA (CP-286) and -100 into
EU@AI2 RA (CP-287). Enter 10 into AI2 RB (CP-288) and 100 into EU@AI2 RB (CP-289). AI2 Mode
(CP-285) should be set to volts (1).
The scaled range of the Auxiliary Analog Input 2 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 in 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 AI2 RA (CP-286) equal
to AnlgCal Ref A (MP-168) for this signal and set AI2 RB (CP-288) 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 AI2 RA and AI2 RB into AnalogRef Val (CP-463) for
the two points of operation/calibration. Enter the EU corresponding to these two points into EU@AI2 RA
and EU@AI2 RB after the calibration is completed. Refer to Drive Setup/Calibration: Calibration for
additional details. For the formulas for the Auxiliary Analog Input 2 calculations, refer to Appendices:
Appendix B.