12 Operation
HP289
3.2.2 Signal Timeout
The Signal Timeout period defines a time interval which is used to
detect if the flow has stopped. If there is no signal input for a time
greater than the Signal Timeout period the flow is deemed to have
stopped. The Signal Timeout period has two functions:
• To detect the loss of signal during a batch when the relays are
energized. In this case, the Batcher will enter a Flow Alarm
condition and de-energize the relays.
• After the preset batch quantity has been reached and the relays
de-energize, some overrun of flow may occur due to slow
valve closure, etc. In this case, the Signal Timeout is used to
determine when the flow has ceased and thereby accurately
determine the amount of overrun.
It is recommended that Signal Timeout periods be kept fairly short, but
long enough such that the timeout period is significantly longer than the
time period between successive input pulses from the flowmeter at the
minimum flowrate.
The instrument enables the user to set a time interval of up to 99
seconds to detect an absence of signal input. If the Signal Timeout is
set to 0, this function is disabled.
Flow Alarm
If a Signal Timeout is set greater than zero and loss of signal is detected
during a batch, a Flow Alarm signal is outputted on terminal 7. In
addition, both control relays are de-energized. The Flow Alarm output
and condition is maintained until acknowledged by pressing the STOP
key. The alarm condition is also signaled to the operator by the
flashing STOP LED. Once acknowledged, the process can then be
reset via the STOP key or continued by pressing the RUN key.