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IP2046/IM
Nov 2006
APPENDIX D
HART COMMUNICATIONS WITH THE MSP400
D 1.0 Overview
The MSP400 ultrasonic level transmitter supports HART communications, which may be used to
programme or interrogate the transmitter remotely from any point on the 2 wire loop.
Any HART compatible communication device may be connected across the loop and, if loaded with the
Device Description (DD) of the MSP400 transmitter, will have full access to the all of the parameters of
the instrument as shown in D 3.0
If the communication device is not loaded with the MSP400 DD, then access to the Universal and some
Common Practice commands is possible in accordance with HART convention.
The MSP400 may be used with the Mobrey MCU900 Series of control units. MCU900 will
supply the 24V dc loop power to the MSP400 and provide control functionality using the 4-20mA signal
from the transmitter.
The MCU900 control unit has HART communications capability and access to all of the parameters of the
MSP400 as shown in D3.0.
The Mobrey PC software “DDConf” is also available, allowing a computer fitted with
a HART modem to communicate with and re-programme the MSP400 transmitter.
Note : A HART modem is supplied with the DDConf software.
D 2.0 Wiring
Wiring for HART communications is no different to that of 4-20mA instruments, except that the loop
must contain a resistance of at least 250 Ohm. This resistance may be achieved by a combination of
wiring resistance and any other loop instruments, or may be achieved by the inclusion of a suitable 250
Ohm resistor, usually connected in series in the +24V dc power line at the power supply.
Note, the MSP400 requires a minimum voltage of 12V dc at the terminals for correct operation.