Setra System Model Datum 2000 - Manual (Page 17)

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For the first pressure point connect the "mA" to gound, pin 8 to pin 9 (CH2:
pin 14 to pin 15). Enter the pressure that corresponds to zero mA input
(since most transmitters are 4 to 20 mA, 0 mA will have a negative value).
Use the following formula (see example):
Full scale pressure – offset pressure
SLOPE = ————————————————————
Full scale mA – offset mA
OFFSET = Pressure ( @ mA ) – (SLOPE x mA)
mA = REFERENCE VOLTAGE / INPUT IMPEDANCE
PRESSURE = (SLOPE x mA) + OFFSET
(DEFINITION OF OFFSET: Offset pressure and offset current (mA) refers to the minimum
pressure input and current output of the transmitter, e.g., a 4-20 mA output, 0 - 50 psi transmit-
ter, the offset current is 4 mA and the offset pressure is 0.)
For the second pressure point, connect the reference voltage (either contact
of the 2 pin blue connector located behind the terminal strip) to the "mA", pin
8 (CH2: pin 14). Enter the pressure that corresponds to this input current
according to the formula above; the value of the reference voltage and the
"mA" input impedance is recorded on the serial label on the bottom of the
DATUM 2000™.
Example:
A 1000 PSI transmitter outputs 4 mA at 0 PSI and 20 mA at 1000 psi. The
DATUM 2000™ has a reference voltage of 2.4995 and channel 1 input
impedance is 149.01 ohms.
1000 – 0
SLOPE = ————— = 62.5
20 – 4
OFFSET = 0 – 62.5 x 4 = -250
PRESSURE (@0) = 62.5 x 0 – 250 = –250
mA = 2.4995/149.01 = 16.774 mA (0.016774 Amps)
PRESSURE (@ REF) = 62.5 x 16.774 – 250 = 798.4