34
INM4500-2
Mar 2009
6.4.2 MTL4549/4549C/4549Y - Isolating Driver
Two channel, for 4/20mA smart valve positioners with line fault detection
The MTL4549 accepts 4/20mA fl oating signals from safe-area controllers to drive 2 current/pressure
converters (or any other load up to 800
Ω
) in a hazardous area. For smart 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 fi eld wiring: if these
occur, the current taken into the terminals drops to a preset level. The MTL4549C and MTL4549Y
are identical to the MTL4549 except that they provide open circuit detection only (no short-circuit
detection).
Hazardous area
Safe area
P
I
P
I
1 2 3 4 5 6
7 8 9 10 1112
13 14
I
I
I
I
Vs+
Vs
2035V dc
Ch 1
4/20mA
+
+
Ch 2
+
+
Ch 1
Ch 2
4/20mA
4/20mA
Terminal
Function
1
Output –ve (Ch 1)
2
ve (Ch 1)
4
Output –ve (Ch 2)
5
ve (Ch 2)
8
Input –ve (Ch 1)
9
Input +ve (Ch 1)
11
Input –ve (Ch 2)
12
Input +ve (Ch 2)
13
Supply
–ve
14
Supply
+ve
Figure 6.24
LED indicators
for MTL4549,
MTL4549C &
MTL4549Y
PWR
MTL4549Y
PWR
MTL4549
PWR
MTL4549C