Brooks Instrument MT3810 - Manual (Page 46)

3-8
Model MT 3810
Installation and Operation Manual
X-VA-MT3810-eng
Part Number: 541B050AAG
December, 2008
Section 3 Operation
Computations: Totalization
Totalizers are available in both Resettable and Inventory options.
Resettable totalization is used for batching while inventory totalization
measures the total volume over time. Units of measure are set indepen-
dently for each of these options.
Pulse Output: Pulse Out Scaler, Pulse Out Width
The SMM has a pulse output channel that indicates flow rate as a variable
frequency and therefore can pass information to many types of external
equipment such as batch controllers, automation systems or provers. The
output pulse width default is 1 millisec but may be user-configured since
certain external receiving equipment cannot keep up with high incoming
frequency.
Low Flow Cutoff Warning for Pulse Output and Totalization
The low flow cutoff parameter can be programmed to signal when the flow
level is below which the process is intended. Below this level, the totalizer
will assume that the flow rate is actually zero and that no data should be
accumulated by the totalizers.
Pulse Output Overrun Alarm
If a larger than acceptable output pulse width is configured, totalizer pulses
may be delayed or queued. No loss of pulses will occur. The totalizer
output pulses will to be sent until the queue is empty. Under these circum-
stances, an alarm message will be sent to the control station. However, the
alarm can be disabled if not required.
Optional Alarm Configurations— Enable, Destination, Alarm Type (Latching)
Three additional parameters may be programmed for process and diag-
nostic alarms to control functionality — enable, destination, and alarm type
(latching). ‘Enable’ allows alarms to be enabled and disabled depending on
use of the alarm. For example, if output pulses are being used it may be
normal practice to delay (e.g. queue up) output pulses because of a slow
receiving end-device that requires a wide pulse-width. The ‘enable’ param-
eter allows the user to disable the pulse output overrun alarm and not send
an alarm when in fact pulse outputs are delayed by choice. Some critical
diagnostic alarms, such as database initialization, can not be disabled or
turned off.
When an alarm occurs, it can be posted through the defined 'destination'
digital contact closure outputs #1, #2, both or neither. Therefore the alarms
may be managed according to local operating practices and the need to
notify upstream control/safety systems.
An alarm may be posted at a designated destination only when the alarm
situation is occuring or posted until the alarm is acknowledged by the
operator. The descision to 'latch or unlatch' the alarm is controlled by
setting the 'alarm type' parameter. By utilizing this optional parameter, the
operator can see that there is an alarm as it is occuring (unlatched) or
even after the fact, in the case when the operator did not directly observe
the unit alarm (latched).