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CURS100 100 Ohm Current Shunt Terminal Input Module

The transducer will output 4 mA at 200 psi and 20 mA at 700 psi. Using Ohm's

law, the voltage across the resistor at 200 psi is:

V = I  R

V = 0.004  100

V = 0.4 V or 400 mV

and at 700 psi is:

V = 0.020  100

V = 2.0 V or 2000 mV

Since the datalogger measures in mV, the multiplier (or slope) must be in units of

psi/mV. Therefore, the y values have the units psi and the x values mV.

The equation of a line is:

(y ─ y

) = m (x ─ x

)

Solve the equation for m that is the slope of the line (or multiplier).

psi psi

mV mV

psi







700 200

2000 400

0 3125.

Now replace the known values to determine the intercept (or offset). Where y =

m(x) + b

psib

bmV

psi

754003125.0200

4003125.0200





m = multiplier (slope) = 0.3125 and

b = the offset (intercept) = 75.0.

5.3 CR1000 Program Example

'CR1000 program example for sensor with 4-20mA output.

'Assuming a flow meter that outputs a 4-20mA signal representing 0 - 100 gal/min,

'the voltage across the resistor at 0 gal/min = 4mA * 100 ohms = 400mV,

'and at 100 gal/min is 20mA * 100 ohms = 2000mV. The change in mV is

'2000mV - 400mV = 1600mV for 0 - 100 gal/min flow rate.

'The measurement result (X) for the VoltDiff instruction is mV. The

'multiplier to convert mV to gal/min is: mV * 100gal/min / 1600mV = 0.0625,

'the offset is 400mV * .0625 = -25.0.

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Campbell CURS100 Manual de usuario Pagina 16

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