46
6.5 Analogue Output modules
The analogue output (AO) modules accept 4/20mA floating signals from safe-area controllers to
drive current/pressure converters (or any other load up to 800Ω) in a hazardous area.
6.5.1 MTL5546/MTL5546Y(-T) - Isolating Driver
Single channel, for 4/20mA HART® valve positioners with line-fault detection
The MTL5546 accepts a 4/20mA floating signal from a safe-area controller to drive a current/
pressure converter (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
MTL5546Y(-T) is very similar to the MTL5546 except that it provides open circuit detection only
(i.e. no short-circuit detection).
Hazardous area
Safe
are
a
Terminal Function
1 Output –ve
2 Output +ve
11 Input –ve
12 Input +ve
13 Supply –ve
14 Supply +ve
Input characteristics
Field wiring state MTL5546 MTL5546Y
Normal <6.0V <6.0V
Open-circuit <0.9mA <0.5mA
Short-circuit <0.9mA N.A.
Figure 6.25:
Top labels
for MTL5546
& MTL5546Y
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