SM500F
Field mountable paperless recorder
2 Installation
18
IM/SM500F Rev. Z
2.4 Single Analog/Digital Inputs
2.4.1 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.
2.4.2 Resistance Thermometer (RTD)
On applications requiring long leads it is preferable to use a 3-lead resistance thermometer.
If 2-lead resistance thermometers are used, each input must be calibrated to take account of the lead
resistance.
Fig. 2.9 Single 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
1 2 3 4
+
Thermocouple
1 2 3 4
+
Voltage
+
1 2 3 4
3-lead RTD
White
Red
Red
1 2 3 4
+
Thir
d Lead
4-lead RTD
1 2 3 4
Each lead must be of equal
resistance and less than 10
W
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.
