American Magnetics 135 & 136 Liquid Helium Level Instruments (CE-Marked) - Manual (Page 63)

Rev. 3 51
Service Guide
Unit not responding to communications
6.1.4 Unit not responding to communications
1. Verify your communications cable integrity and wiring. See the
Appendix for DB-25 to DB-9 translation for RS-232 cables.
2. Check to make sure you are sending the correct termination to the
instrument. If you are using the RS-232 option, make sure the echo
feature is set correctly for your application and the baud rate
matches the setting of the host device. If you are using the IEEE-
488 option, check the primary address setting and make sure the
controller software is set to query the instrument at the primary
address selected.
3. Check your host communications software and make sure it is
recognizing the return termination characters from the instrument.
For RS-232 communication, the return termination characters are
<CR><LF>. For IEEE-488, the return message termination
characters are <LF> with EOI.
4. If the instrument is responding repeatedly with -8 as the return
message, try a device clear command (DCL) or powering the
instrument off and then back on. Be sure you are sending valid
commands.
5. If you experience continued trouble with the IEEE-488 option, you
may have an incompatible IEEE-488 card in your host computer. In
the past, AMI has found subtle differences between manufacturers
of IEEE-488 cards that have introduced communication errors.
AMI attempts to establish compatibility with as many products as
possible, however, it is difficult to test every card available. Contact
AMI directly if you have thoroughly checked your setup and
continue to experience problems with the IEEE-488 option.
6. Version 2.6 of the NI-488.2 drivers from National Instruments has
known bugs that prevent the correct operation of the IEEE-488
interface when executed from LabVIEW. Contact National
Instruments for workarounds appropriate for your configuration.
If the cause of the problem cannot be located, contact an AMI customer
service representative for assistance. DO NOT SEND A UNIT BACK TO
AMI WITHOUT PRIOR RETURN AUTHORIZATION.