DRAFT - 11 December 2014
DRAFT - 11 December 2014
12
DRAFT - 11 December 2014
INM MTL4850_54 Rev4
4.4 HCU16AO HART connection unit
Many older instruments have 4-20mA analogue outputs that are not compatible with HART
data because their impedance is normally too low for the HART to operate correctly. In
addition, the noise generated by the analogue output can sometimes interfere with the HART
data, or sometimes the HART signal can even affect the stability of the current signal.
The HCU16AO HART connection unit - see Figure 4.8 & 4.9 - enables HART signals to be used
in current output loops, in non-hazardous areas. It has 16 isolated channels, each with a low-
pass filter in series with the current signal from the system. This has virtually no effect on the
4-20mA signals but presents a suitable high impedance (> 240
W
) to the HART signals for their
detection and measurement.
Field and system connections are made via pluggable 8-way, screw-clamp terminals, in 4
groups of 4 channels.
4.4.1
Mounting
The HCU16AO is designed for mounting in a control room equipment cabinet and is supplied
fitted on a carrier suitable for T or G section DIN-rail mounting in any orientation.
Carrier weight:
770g (nominal)
Footprint dimensions:
See Figure 4.8
Height:
58mm from top of DIN rail to top of screw connectors
4.4.2
Ribbon cable connector
A 20-way ribbon cable connector is provided on the HCU16AO to link to the HMP-HM64.
Figure 4.8
HCU16AO
connection unit
