SENSOR CONNECTIONS
The sensor connections are on the left side of the terminal enclosure.
Each sensor has two screened twisted wire pairs, either as one dual pair cable, or two separate pairs
One pair is connected to the TX (transmit) group and the other to the RX (receive) group. The sensors are symmetrical so either of the pairs can be chosen as TX or RX. The two cores in each group are connected to A and B, the polarity is not important. Each screen connection, normally coloured green, is connected to the group’s SCN terminal. Cable screens must not be earthed at any other point.
The
RELAYS
The relay
HART CONNECTIONS AND JUMPER SETTINGS
There are two clearly labelled HART Test Points, labelled A and B. These test points are for connection of a HART Hand Held Communicator, to provide a local interface to the MSM400 if required. Above terminal blocks
The normal position is with the plug shorting out the left hand pins. In this case, the external 20 mA loop must have at least a 250 ohm impedance to enable HART communictions. With the plug in the central position, the MSM400 itself provides this load in the 20 mA loop. The right hand position enables HART communication when there is no external loop connected by connecting a 270 ohm resistor across the current output. (See Appendix D).
NOTE:
The 20 mA output will not function correctly when the link is in this right hand position, so replace it in position 1 or 2 after use!
CURRENT OUTPUT
The current output may be connected in
In
Note that the current output must not be routed through hazardous areas unless protected by an additional I.S. barrier.
Terminal Number
Figure 10 : Alternative current output configurations
IP258
14
