Campbell Scientific CS440 Liquid Level Sensor - Manual (Page 9)

CS440 Liquid Level Sensor
5
Multiplier and Offset
The Multiplier and Offset can be changed to scale the result or perform unit
conversions. The VoltSE instruction measures mVolts.
V=IR
At 4 mA, V = 4 mA * 100 ohms = 400 mV
At 20 mA, V = 20 mA * 100 = 2000 mV
Pressure = M * mV output + b
Where; M = multiplier, and b = offset
M= Pressure range / (mV2 – mV1)
If the sensor outputs 0 psi at 4 mA (or 400 mV), and 5 psi at 20 mA
(or 2000 mV) then the multipliers is calculated as follows for a 50 psi
sensor:
M = 50 psi / (2000 mV – 400 mV) = 0.03125 psi/mV
To convert to depth in feet., (Depth = 2.31 * psi).
M = 0.03125 psi/mV * 2.31 ft/psi = 0.7218 ft mV
The offset is typically applied in the field to adjust the reading to
whatever datum is used.
5.3 Using Edlog
Typically, Instruction 2 (Volt Diff) is used to read the CS440. Instruction 1
(Volt SE) can also be used to read the CS440. Your datalogger manual
provides detailed explanations of Instruction 1 and Instruction 2.
;{CR10X}
;
*Table 1 Program
01: 60
Execution Interval (seconds)
1: Volt Diff (P2)
1: 1
Reps
2: 25 2500 mV 60 HZ rejection
3: 1 Channel
4: 1 Loc [ Level ]
5: .7218 Mult
6: 0.0 Offset
*Table 2 Program
02: 0.0000 Execution
Interval (seconds)
*Table 3 Subroutines
End Program