Brooks Instrument MT3809G - Manual (Page 43)

Installation and Operation Manual
X-VA-MT3809G-MT3810G-eng
Part Number: 541B182AAG
September, 2013
Models MT3809G & MT3810G
3-5
Section 3 Operation
The alarms may be set at the minimum and maximum flow rate or at any
other preferred high and low limits. The units of measure of the alarm limits
are the same units of measure as the process variable itself.
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 independently for each of
these options.
Pulse output: Pulse out scaler, pulse out width
The transmitter 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
circumstances, 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
diagnostic 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’ parameter 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 occurring or posted until the alarm is acknowledged by the
operator. The decision 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 occurring (unlatched) or even after
the fact, in the case when the operator did not directly observe the unit
alarm (latched).