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6 .5 .2
Two channel, for 4/20mA HART® valve positioners with line-fault detection
The MTL5549 accepts 4/20mA floating signals from safe-area controllers to drive 2 current/
pressure converters (or any other load up to 800Ω) in a hazardous area. For HART valve
positioners, the module also permits bi-directional transmission of digital communication
signals so that the device can be interrogated either from the operator station or by a hand-held
communicator. Process controllers with a readback facility can detect open or short circuits in
the field wiring: if these occur, the current taken into the terminals drops to a preset level. The
MTL5549Y is very similar to the MTL5549 except that it provides open circuit detection only
(i.e. no short-circuit detection).
MTL5549
PWR
MTL5549Y
PWR
Figure 6 .26:
Top labels
for MTL5549
& MTL5549Y
48
MTL5549/ MTL5549Y - Isolating Driver
Hazardous area
Safe area
Ch 2
+
P
4/20mA
I
–
+
P
4/20mA
I
–
Ch 1
Terminal
Function
1
Output –ve (Ch 1)
2
Output +ve (Ch 1)
4
Output –ve (Ch 2)
5
Output +ve (Ch 2)
8
Input –ve (Ch 2)
9
Input +ve (Ch 2)
11
Input –ve (Ch 1)
12
Input +ve (Ch 1)
13
Supply –ve
14
Supply +ve
Input characteristics
Field wiring state
Normal
Open-circuit
Short-circuit
6
7
I
–
5
8
4/20mA
4
9
I
+
10
3
I
–
11
2
4/20mA
12
I
1
+
13
14
20 to 35V dc
MTL5549
MTL5549Y
<6.0V
<0.9mA
<0.5mA
<0.9mA
Ch 2
Ch 1
Vs–
Vs+
<6.0V
N.A.
INM 5500 Rev 11
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