35
INM4500-2
Mar 2009
6.5 Temperature Input module
The MTL4575 module accepts inputs from low-level dc sources such as thermocouples or RTDs in
hazardous areas and converts them into 4/20mA signals to drive safe area loads.
6.5.1 MTL4575 - Temperature Converter
THC or RTD input with alarm
The MTL4575 converts a low-level dc signal from a temperature sensor mounted in a hazardous
area into a 4/20mA current for driving a safe-area load. Software selectable features include
linearisation, ranging, monitoring, testing and tagging for all thermocouple types and 2, 3 or
4-wire RTDs. (For thermocouple applications the HAZ-CJC plug, on terminals 1–3, includes an
integral CJC sensor). Confi guration is carried out using a personal computer - see next page. A
single alarm output is provided and may be confi gured for high or low process alarm or to provide
notice of early thermocouple failure.
Safe area
1 2 3 4 5 6
7 8 9 10 1112
13 14
I
mV
Vs+
Vs
2035V dc
+
Load
4/20mA
+
mV
4-wire
3-wire
Alarm
Configuration
socket
Terminal
Function
1
THC/EMF/RTD
input
–ve
3
THC/EMF/RTD
input
+ve
4
3-wire RTD input –ve
5
4-wire RTD input +ve
8
Output
–ve
9
Output
+ve
11
Output –ve/Alarm relay
12
Alarm
relay
13
Supply
–ve
14
Supply
+ve
Hazardous area
Early burnout detection (EBD)
When EBD is selected, the resistor of the thermocouple circuit is monitored and an alarm is raised
when there is an increase of more than 50
Ω
. This enables preventative maintenance to be conducted
on the fi eld installation before the thermocouple actually breaks.
Figure 6.23
LED indicators
for MTL4575
PWR
STS
MTL4575
CONFIG
