Watlow CAS - Manual (Page 86)

76 CAS User’s Guide
Appendix: Linear Scaling Examples
Example 2
Situation
A flow sensor connected to the CAS measures the flow in a pipe. The
sensor generates a 0-5V signal. The sensor's output depends on its
installation. Independent calibration measurements of the flow in the
pipe indicate that the sensor generates 0.5 volts at three gallons per
minute (GPM) and 4.75 volts at 65 GPM. The calibration instruments
are precise to ±1 gallon per minute.
Setup
The sensor is connected to a channel input set up with a resistor voltage
divider network to produce 60 millivolts at 5 volts. (See the Inputs
section of the Installation chapter for information on scaling networks.)
The calibrating instrument is precise to ±1 gallon per minute, so the
appropriate display format is -999 to +3000.
This table shows the input readings.
The scaling values are therefore:
PV
Displayed
Sensor Input Reading (%FS)
65 GPM 4.75 (4.75 V/ 5.00 V) x 100% = 95%
3 GPM 0.5 (0.5 V/ 5.00 V) x 100% = 10%
Parameter Low Value High Value
Process Value (PV) 3 GPM 65 GPM
Input Reading 10.0 95.0