26
Problem
Probable Cause
What to do
PCOMTEST
program works
continuously but
TXD LED of PC
COMPORT does not
flash
1. PC COMPORT
number is not
correct
2. PC COMPORT
setting uncorrected
3. PC COMPORT is
damaged
Change COMPORT
number (setup of
PCOMTEST);
Check COMPORT
card setting;
Change COMPORT
card
Instrument RXD LED
does not flash
Communication cable
not connected
properly
Check cable
Instrument TXD LED
does not flash
Instrument
COMPORT setting is
not correct
Check that instrument
& PC COMPORT
settings match:
RS Standard
Address
Data Format
Baud rate
Protocol name (ASCII
or non-ASCII)
PC COMPORT RXD
LED does not flash
Communication cable
not connected
properly
Check cable
Instrument does not
respond more than
1% of sessions in
the ASCII or non-
ASCII test
1. ON the
communication
line there are a
few instruments
with the same
address or
instruments with
address zero
2. Analog expander
outputs are
allocated on the
one of the
instruments
1. Check every
instrument
separately
2. Cancel the analog
outputs if analog
expander is not
used
PCOMTEST
receives reply from
the instrument with
an incorrect check
sum
Problems with the
communication lines
Check the
communication line:
Wires must be more
than 0.33 mm
2
/ 22
AWG
Grounded screen
Terminated resistors
Communication line
Distance < 1200 m
