Operation Of Reed Switch Alarm - Brooks Instrument Ar-Mite MT3750 Manuel D'installation Et D'opération

Section 3 Operation
®
Brooks Ar-Mite

3-4 Operation of Reed Switch Alarm

3-2
TM
MT3750C
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 con-
nected 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 maxi-
mum 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.
Installation and Operation Manual
X-VA-MT3750C-eng
Part Number: 541B063AAG
October, 2013