SM500F
Field mountable paperless recorder
2 Installation
IM/SM500F Rev. Z
19
2.5 Dual Analog/Digital Inputs
2.5.1 Thermocouple
Use the correct compensating cable between the thermocouple and the terminals – see Table 2.1,
page 20.
Automatic cold junction compensation (ACJC) is incorporated but an independent cold (reference) junction
may be used.
Fig. 2.10 Dual Analog/Digital Input Connections
Note.
Analog/digital input terminal screws must be tightened to a torque of 0.5 Nm (4.5 lbf.in).
Current
Thermocouple
1 2 3 4
+
Voltage
+
+
1 2 3 4
Digital Input
(Volt free or 24V)
Logic state inactive
Logic state active
1 2 3 4
+
+
*
*
In the powered-down condition the current input
is open circuit. In order to maintain a current loop
when the unit is powered down, fit a zener diode
(BZX79 B/C2V4) to the input as shown.
Input 1 Input 2
Input 1 Input 2
+
*
Input 1 Input 2
+
1 2 3 4
Input 1 Input 2
+
