3-6
3.2 Zero/Span Adjustment
The zero/span adjustment method that uses an external zero/span adjusting mechanism
will now be described.
[Adjustment Method]
The zero/span adjustment screw functions as an on/off switch. When rotated 90° clock-
wise, the UP switch turns on, when rotated 90° counterclockwise, the DOWN switch
turns on, and when returned to the original position, both switches turn off. Adjust the
position by repeatedly turning this switch on and off. The position of the feedback lever
is stored when the switch is turned off. Since zero point and span point adjustments do
not interfere with each other, these can be adjusted independently.
The operation of the external zero/span adjustment unit is shown below.
[Adjustment Direction]
When the adjustment screw is turned in the clockwise direction, the feedback lever
moves in the upward direction.
Figure 3-2-1. Adjusting the Lever in the Upward Direction
When the adjustment screw is turned in the counterclockwise direction, the feedback
lever moves in the downward direction.
Figure 3-2-2. Adjusting the Lever in the Downward Direction
Note
• The external zero/span adjustment mechanism uses a magnet to turn a reed switch
on and off.
• Do not use a magnetic screwdriver, as this may prevent the function from operat-
ing.
• The external zero/span adjustment function determines, based on the input signal,
whether a valve fully open position (span) adjustment or a valve fully closed posi-
tion (zero) adjustment is to be performed. If the input signal is not within a range
of ±1 mA of the electric current setting values that correspond to the valve open
and closed positions, this function will not operate.
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