Yokogawa 414 Batch Controller - Manual (Page 17)

Operation 15
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. A Signal Timeout period has
two functions:
♦ To detect the loss of signal midway through a batch when the relays are
energised. In this case, the Batcher will enter a Flow Alarm condition and
de-energise the relays.
♦ After the preset batch quantity has been reached and the relays de-
energised, 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 are kept fairly short, but long
enough such that the 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 program 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 the Signal Timeout is set at greater than 0, and loss of signal is detected midway
through a batch, a Flow Alarm condition exits and both relays are de-energised.
The Flow Alarm condition is maintained until acknowledged by pressing the STOP
switch. The alarm condition is also signalled to the operator by the flashing STOP
LED. Once acknowledged, process can
then be reset via the STOP switch or continued by pressing the RUN key.
With the Model 414D, an open collector output on terminal 7 will also switch "On"
whenever the Flow Alarm condition exists (see Section 3.5).