Watlow ANASCAN User Manual download pdf (Page 59)

ANASCAN User’s Guide 51

APPENDIX: Input Scaling

All inputs use the automatic scaling function of the Mx+B calculation.

The end points of that calculation are set by HiPV, LoPV, HiRDG, and

LoRDG. The default values are set by the input Type selection. Do not

adjust these values until you completely understand what those

adjustments will do.

The T/C ranges are set in the firmware, and you don’t need to adjust

those ranges for a proper operating hardware or software. The default

values provide correct operating parameters as to stated accuracy and

Alarm settings.

For Linear inputs the scaling of the input is required to obtain correct

engineering units of the input. This must be done before setting SP and

Alarm settings.

Linear Input Scaling

A linear input of 60 mv or less is scaled according to the engineering

unit and mv range of the input signal. The CAS has a -10 to 60 mvdc

analog input range. All linear inputs must be scaled to that range by

scaling resistors on the input.

The HiPV and LoPV is the range of the engineering unit, while the

HiRDG is the % of the Hi end signal level mv with reference to 60 mv

and the LoRDG is the % of the Lo end signal level with reference to 60

mv.

Example 1

Situation

A pressure sensor that generates a 4-20 milliamp signal is connected to

the CAS. The specifications of the sensor state that it generates 4

milliamps at 0.0 PSI and 20 mA at 50.0 PSI.

Setup

The sensor is connected to a channel input set up with a resistor scaling

network to produce 60 millivolts at 20 mA. (See the Inputs section of

the Installation section of this manual for more information on scaling

networks.)

The sensor measures PSI in tenths, so the appropriate display format is -

999.9 to +3000.0.

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Watlow ANASCAN User Manual Page 59