17
Slope
=
1000 - 0
= 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
For the first pressure point connect the "mA" to ground, 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):
Slope
=
Full scale pressure - offset pressure
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 (mA) refers to the minimum
pressure input and current output of the transducer, e.g., a 4-20 mA output, 0-50
psi transmitter, 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™.
1st 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.
