Watlow ANASCAN - Manual (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.