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7.4 Temperature Display Hold
The 9140 has a display hold function which allows action of an external switch
to freeze the displayed temperature and stop the set-point from scanning. This
is useful for testing thermal switches and cutouts. This section explains the
functions available for operating the temperature hold feature. An example fol
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lows showing how to set up and use the hold feature to test a switch.
7.4.1 Hold Temperature Display
The hold feature is enabled by simply pressing the “UP” button. The hold tem
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perature display shows the hold temperature on the right and the switch status
on the left. For the status “c” means the switch is closed and “o” means the
switch is open. The status flashes when the switch is in its active position (op
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posite the normal position). The hold temperature shows what the temperature
of the well was when the switch changed from its normal position to its active
position. While the switch is in the normal position the hold temperature will
follow the well temperature. Operation of the hold temperature display is out
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lined below.
143.5 C
Well temperature display
U
Access hold display
c 144.8
Switch status and hold temperature
To return to the normal well temperature display press “DOWN”.
7.4.2 Mode Setting
The Hold Function is always in the automatic mode. In this mode the normal
position is set to whatever the switch position is when the set-point is changed.
For example, if the switch is currently open when the set-point is changed, the
closed position then becomes the new active position. The normal position is
set automatically under any of the following conditions, (1) a new set-point
number is selected, (2) the set-point value is changed, (3) a new set-point is set
through the communications channels.
The operating mode of the temperature hold is set in the primary menu after the
scan rate setting.
7.4.3 Switch Wiring
The thermal switch or cutout is wired to the calibrator at the two terminals in
the front of the dry-well calibrator labeled “SWITCH HOLD”. The switch
wires may be connected to the terminals either way. Internally the black termi
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nal connects to ground. The red terminal connects to +5V through a 100 kΩ re
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25
7 Controller Operation
Temperature Display Hold