Samsung MR-DH00 Technical Data Book page 135

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COM Check
Check
When pulse input is detected during the test period, the channel numbers are displayed.
Otherwise, the character 'X' is displayed on the corresponding channel position.
Make a loopback connection between COM1 and COM2 to check if the DMS2
communication channel is working or not. Care must be taken for the connection polarity.
When the COM1 communication channel is normal, the message 'OK' is displayed on the
LCD window.
It checks if the pulse width values of actually connected meter are valid or not.
(M:####msec) will be displayed. #### represents the duration of the high pulse.
calculation will start after the check and returning to the upper menu.
3.3 Pulse Width
CH1 Check OK
CH1 Check End
NG (M:0000msec)
Description
CH1 Check Start
Checking...
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