Ma Current Inputs; Figure 1-3. Resistor Table, Di Inputs - Brainboxes AD-945 Supplementary Manual

Reference
these are 10k 1/4 watt nominal value, though anything in the
range 1k-100k would be adequate. Installing these resistors
causes the return side of each channel to be referenced to the
system ground, SYS GND. The return resistors for channels 0 to
7 are R14, R10, R6, R2, R15, R11, R7 and R3 respectively. See
Figure 1-3.
________________________________

Figure 1-3. Resistor Table, DI Inputs.

Function
Thermocouple
Open Circuit
Detection
Differential
Return Path
To Analog Gnd
4-20mA
Current Shunt R13
(0-5V input)
*NOTE: R26 NOT REQUIRED WHEN CJC CIRCUITRY IS BEING USED.
_____________________

4-20mA Current Inputs.

The 4-20mA current input scheme is commonly used in
industry. 4-20mA currents are inherently differential inputs since
current flow round a CIRCUIT there is the current terminal and
its return line, there the AD1200 card will be configured for 8
DI inputs. Currents can be sent a long way without degradation
(there is Law of Conservation of Current but no Law of
Conservation of Voltage) and are remarkably free of interference.
The AD1200 series have voltage inputs so the the 4-20mA
current inputs have to be turned into voltages for the A/D card
to be able to convert the signals. When a current passes through
a resistor a voltage is generated and this is the simple basis for
Page 4
Resistors 8 DI Differential Inputting
0 1
R26 R27 R28
*NOTE
R14 R10 R6
R9 R5
Analog Terminal Board
2 3 4
R29 R30
R2 R15
R1 R16
5 6 7
R31 R32 R33 100M
R11 R7 R3
R12 R8 R4
Ohms
10k
250R
%tol
0.01