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Electronics
8
Interfacing to external devices
System ready
When interfacing to an external device, it is often desirable to send a system ready
signal to the device. In the case of a multi-sample Tekmar purge-and-trap, each
sample is purged onto a trap where it waits for a ready signal. On receipt of the
ready signal, the desorbtion cycle begins. When a specific temperature has been
reached, the purge-and-trap closes a contact to indicate the run has started.
The ready pin on the remote start connector on the GC is held low at all times
except when the GC, MSD, and data system are all ready. On system ready, a logic
high of 5 V dc is present between that pin and any ground. This same high can be
detected between the ready and ground pins on the remote start connector on
the MSD.
Start run input
The best way to generate a start run signal is to use the remote start connector on
the GC. Since remote start cables are made for most common devices, this is often
the simplest way. A general-purpose remote start cable (05890-61080), which is
also available, terminates in spade lugs. Care must be taken to ensure that the sys-
tem is actually ready before the start run signal is sent.
If necessary, the remote start connector on the back of the MSD can be used to
send the start run signal. A contact closure between the start and ground pins will
start the run if the system is ready.
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