Ametek Drexelbrook Impulse GW Series, Installation And Operating Instructions Manual, Page: 89 / 99

Troubleshooting
83
6.3 Troubleshooting the Loop Connections (Continued)
Is loop
current
between 3.7 and
22 mA?
Is there a
minmum of 250
ohms loop
resistance?
Are you connected
to a DCS?
Is It Polling?
Make it stop polling or power
transmitter from a separate
source - then re-check
operation.
Yes
Yes
Yes
Check:
1. Is correct
COM Port selected at startup?
2. Is there any software running that would re-direct COM Port such as
Windows, mouse drivers, terminal emulation software, or TSR's.
3. Possible bad RS-232 cable or defective modem.
4. Check modem connections to loop
Modem does
not
communicate
with
transmitter.
No
No
Start
No
Are you using
the Drexelbrook
supplied modem?
Check:
1. Is modem non-isolated
from ground and/or is your
laptop plugged into AC
power.? If so you may have
ground problem. Contact
Service department.
2. Some laptops don't provide
enough voltage to drive
modem correctly from
COM Port. Check with
modem supplier or try a
different laptop.
3. Checkout "Yes" response
tests listed below.
No
Yes
Check:
1. If loop current is 0 mA, check polarity of loop at
transmitter. If it is OK, check for open loop.
2. If loop current is between 0 and 3 mA transmitter is
likely bad.
3. Check voltage at transmitter it should be at least 12
4. Disconnect transmitter from power supply and verify
volts when 20 mA is flowing in the loop.
power supply voltage is correct, 24 VDC Typical.
No
Yes
1. Check Power Supply and loop source
resistance (the 250 ohms may be built in as
with the Drexelbrook 401-500 series or most
DCS inputs).
2. If not there add enough resistance for loop to
be at least 250 ohms.
1. Check calibrator connections to loop per loop drawing.
2. Check for "noise" and ripple on loop with oscilloscope. Maximum noise level per HART
Foundation is 1.2 mV rms (500 - 10 kHz). Maximum ripple (47 - 125 Hz) specification is .2V p-p. Line
noise can sometimes be traced to things like motor speed controller wiring in close proximity with
transmitter. Noise can sometimes be overcome by increasing loop resistance thereby increasing
calibrator signal. Noise effects can also be reduced by connecting calibrator directly at
transmitter. Generally noise is only a problem when calibrator is communicating with transmitter
and does not affect normal operation of transmitter.
3. Check voltage at transmitter. It should be at least 12 volts when 20 mA is flowing in the loop.