4.6.1: Voltage Connections
Voltage can easily be monitored using a variety of instrumentation such as
voltmeters. Voltage drops along wires contribute to measurement errors, so care
must be taken when using long cable lengths (100 m for example). High imped-
ance instruments are more prone to interference.
Power Supply
0V
+ 10-30 V
0V
+VE
0V
Vout
Iout
Process M onitor
+
-
Voltage
The signal 0 V should always be used as reference. If power supply 0 V is used,
then error voltages may be introduced.
4.6.2: Current Connections
Current output requires the use of purposely designed current input instrumenta-
tion. Current output is more suitable for transmitting over longer distances be-
cause current is not lost due to wiring resistance. Additionally, with a low imped-
ance, a current loop is less likely to pick up noise.
Iout
Vout
Power Supply
0V
+ 10-30 V
0V
+VE
0V
Process M onitor
Current
+
-
The total loop resistance (resistance of measuring equipment and wiring) must
not exceed specification.
Note: The LDX-4 is not loop-powered, so a power supply must not be used in-line
with the current output.
