PerkinElmer LS 55, User Manual

Page: 32 / 202

32 . LS 55 User’s Guide
Timed event marks can be recorded by supplying a contact closure between the
OVA
and the
Event Mark
connections, or by using the EVENT button on the
Biokinetic accessory. All FL WinLab software applications which display a
Show
Timed Events
option will respond to the contact closure/button press.
Scan Busy
This is a logic level signal, and follows the status of the LS 55:
• during data collection the Scan Busy line is set high.
• on ending the data collection run the logic level reverts to zero.
This function is particularly critical when an external device is attached and the
instrument can be started by a Remote Start event. The external device should
then monitor the Scan Busy line and not send out a further start signal until the
Scan Busy line shows that data collection is complete.
Since this signal is a logic level, devices requiring a contact closure can be
connected via a small solid-state relay (with a switching diode for anti-bounce).
Optimal connection to external autosamplers
Some commercially available autosamplers can be programmed to send and receive
contact closure signals. Connecting such an autosampler to the LS 55 is
straightforward since the LS 55 can be connected via the Remote Start connectors
(see
Remote starts and event marking
on page 31). This connection, however, only
establishes one-way communication and cannot be considered optimal since the
control system is not closed.
Better control can be achieved by making a closed control loop. Use the Remote
Start to control the LS 55’s measurement and the Scan Busy to control the
autosampler. A typical application of such a control system is shown in
Figure 15.