Brooks Ar-Mite MT3750, Installation & Operation Manual

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Section 3 Operation
Brooks
®
Ar-Mite
TM
MT3750C Brooks
®
Ar-Mite
TM
MT3750C
24
Operation of Reed Switch Alarm
A.Start-up meter as described in Section 3-1
B.Note: The alarm flow ranges specified in Table 3-1 are for reference
only. Normal variations in sensors and meter scales may cause these
values to shift. If the desired performance is not achieved, adjust alarm
for the next nearest flow range and repeat the operation procedure.
Setting the flow rate at which the alarm activates requires placing three
jumpers on the system circuit board and positioning the two sensors.
These combinations are listed in Table 3-1 and in the same table inside
the alarm enclosure. The letters “A” and “B” in the table refer to a
scale imprinted on the sensor bracket. To accurately set the alarm, it is
necessary to establish flow through the meter at a rate corresponding
to the desired set-point.
As an example, set the alarm for switch closure at flow rates below
50% of rated maximum flow. Disconnect any wires which are
connected to the “Alarm Circuit” terminal strip. Connect an ohmmeter
or continuity tester across the printed circuit board terminals marked
“Alarm In” and “LO”. Find, in the table, the row marked “Low Flow
40 - 70%”. Follow the row across to the column marked “Jumpers”.
In this case, the jumpers required are J1, J4, and J6. Simply pull
the jumpers out from their current positions and place them in the
correct three places. Apply flow to the flow meter and adjust for 50%
of rated maximum flow. Loosen the adjustment screw on the lower
sensor holder and move the sensor until it reaches the lowest position
possible on the sensor bracket. On the sensor holders is a white index
line. Loosen the adjustment screw on the upper sensor holder and
move the sensor until the index line is within the region marked “A”.
Watching the ohmmeter, slowly move the upper sensor within this
region until a change in continuity takes place (switch closes or opens).
Tighten the adjustment screw.
Fine adjustment of the set point may be required. Adjust the flow rate
and observe the behavior of the system. Adjust the upper sensor up or
down slightly as required to meet your requirements for accuracy. After
establishing setpoint, operate system over entire flow range to
verify desired alarm performance.
The position of the sensors along the flow tube is the only required
sensor adjustment. Adjustment of the distance between the sensor
and the wall of the flow tube is made at the factory. This setting
should not be altered.
C.Two jumper configurations allow simultaneous use of both the high and