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4.2
Inputs and Outputs
A variety of inputs and outputs are available on the Sample Sequencer.
4.2.1
Analog Inputs:
Four analog inputs are located on the Sample Sequencer board for reading a 4–20 mA signal from
up to four different analyzers. The Sample Sequencer converts this signal into Engineering Units for
display and outputs the same signal for the Track and Hold analog outputs.
4.2.2
Analyzer Alarm Inputs:
Four analyzer alarm inputs are located on the Sample Sequencer board. These inputs are typically
used to indicate a loss of sample flow to the analyzer. An analyzer alarm will cause the analyzer
description to flash on the operation screen. An analyzer alarm will also cause the digital alarm
output for that sequencer to be set.
When the Sample Sequencer is used in the Continuous mode, an analyzer alarm will immediately
close the active sample valve and open the next sample valve. That sample valve will remain open
until the analyzer alarm clears, one minute elapses, or – if the sum of the sample and flush times is
less than one minute – when the timer expires. After one minute, the Sample Sequencer will open
the next sample valve. The Sample Sequencer will continue trying to establish flow every minute
until the analyzer alarm clears.
When the Sample Sequencer is used in the Batch mode, an analyzer alarm will not immediately
close the active sample valve. Instead, when the analyzer alarm is received, the Sample Sequencer
will start a timeout timer. If the Sample Sequencer does not receive an End of Batch indication from
the analyzer or the alarm does not clear before that timeout timer, the Sample Sequencer will close
the current sample valve and open the next valve in the sequence. If the End of Batch indication is
received before the timeout timer, the Sample Sequencer assumes the alarm is not a loss of flow
and continues with normal operation. The operator can adjust the timeout timer by setting each
sample's Sample Timer.
4.2.3
Calibration Hold Inputs:
Four calibration hold inputs are located on the Sample Sequencer board. These inputs are used to
indicate that the analyzer is performing a calibration. The calibration hold inputs do not perform a
function when the Sample Sequencer is in the Batch mode.
In the Continuous mode, the Sample Sequencer will wait at the active sample with the valve open
when a calibration indication is received. Once the calibration indication clears, the Sample
Sequencer will resume operation entering the Flush state for the sample that was active before the
calibration hold indication was received.
4.2.4
End of Batch Inputs:
Four End of Batch inputs are located on the Sample Sequencer board. These inputs are used to
indicate when a batch type analyzer is finished taking a measurement. Without this input
connected, the Sample Sequencer will never advance to the next sample when the Sample
Sequencer is in the Batch mode. The End of Batch inputs are not used in the Continuous mode.
SPD 5.5.15
Sentry Equipment Corp | Sample Sequencer
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