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D11.2 Trim Current
If the procedure shown above suggests that there is a calibration difference between the MSM400
output and other current monitoring equipment on the loop, it will be necessary to use a calibrated
meter to establish which unit is in error. Using the “Set current” routine of the MSM400 can be
instructed to provide outputs between 4 and 20mA that the MSM400 considers correct. If these are in
error, the “Trim current” routine is used as follows:
The “Trim current” selection sets the current output of the MSM400 either at maximum (supposed to be
20mA) or minimum (supposed to be 4mA) depending on the option selected.
For maximum the display shows:
CURRENT OUTPUT IS
NOW 20mA. MEASURE
CURRENT AND USE ↑ & ↓
TO TRIM THE OUTPUT
Follow the instructions and if the current output is in error, i.e. not 20mA, use the ↑ and ↓ arrows as
trimming signals to adjust the value to be exactly 20mA. Each press of the arrow causes an audible
signal and adjusts the output value by a discrete step. (approx 6μA)
This process should then be repeated for the 4mA setting. Once the current output is seen to be correct
the ON/CLEAR key is used to escape.
Mode Cancelled Warning
If while trimming or fixing the current the analog output returns to its normal mode the message FIXED
CURRENT MODE CANCELLED will be displayed. This could occur for three reasons, master has sent the
appropriate command, the MSM400 has been powered off then on again, or the output in fixed current
mode has been at the same value for 20 minutes.
D.12.0Unknown Instrument
This limited support for unknown control unit is provided so that the identification and basic performance
of any control unit can be obtained without having to change to another HHC. This is of particular use in
multi-drop networks where all the currently occupied addresses need to be identified when selecting an
address for an additional control unit on the loop.
If the control unit detected is not an MSM400, MSP100 or MLT100 then Unknown instrument is
displayed and an access to the parameters is prompted for. If this is selected then the parameters that
are present on all transmitters are uploaded, after first setting up any files that are required.
If the instrument conforms to revision 5 or higher of the HART protocol then the manufacturer of the
instrument will be available. If it is of an earlier revision then only the model number will be available.