I have moved your post to Mass Spectrometry for better visibility. The detector (MSD) shouldn't drop offline even when idle. Since the GC stays connected I do not think this is PC related. You have eliminated the cables as an issue. The ping not being returned is a concern because it tells me that the issue resides within the MSD itself. This could be related to the smart card. I would suggest an onsite visit by an Agilent trained service Representative to troubleshoot this if it becomes more of a problem. With that model of QQQ, a power cycle is the only reset .
It could be a networking issue. Do you know if the gateway IP address is directed to a router or directed straight to the PC?
Reason being we have seen something similar before if there is no fixed IP address on either the PC or the network that is specifically designated for the MS then the connection is "iffy".
Try setting the PC IP configuration from dynamic to fixed to resolve the problem, I would go into start -> cmd prompt, then type IP config to bring up the details. you will need IP address, default gateway, subnet mask.
Then when setting up a new network address to be fixed:
for preffered DNS use something like 126.96.36.199, and 188.8.131.52 for the alternative.
There are also a couple of firmware and onboard code changes that have caused similar issues over the years. It depends on the versions of firmware, smart card OS, PLX board FPGA etc. There are some service notes about these.
The network switch's have also caused some issues over the years but if the GC pings it may not be the cause. Power cycling the switch fixed it some times.
Checking the things gchaplain says is good too! Also check the power setting on your LAN connection and turn off any power saving features.
I would agree with James, you probably should get an onsite visit by an Agilent trained service representative to troubleshoot this if it becomes more of a problem. However intermittent issues are the hardest to troubleshoot!
Dear colleagues! Thank you for your replies!
As a first step, we are trying to check all obvious "cheap" solutions )
I checked PC power options - all at Max (no power saving for CPU, HDD, LAN, "sleep mode" disabled) and LAN/IP settings - static IPs for PC, GC, QQQ (gateway settings are not set). PC configuration check reveals that PC has two LAN-cards but one of them are disabled (PC has no internet or corporate LAN connection). After that I change old HP Procurve 408 switch with relatively fresh TP-Link one and also tested the cables (seem to be OK).
After last rebooting, QQQ works fine. Time will tell...