Manual 82006 Digital Reference Unit
Woodward 5
Setting Ramp Rates
The reference unit is shipped with ramp rates 1 and 2 independently adjustable
from a minimum of 20 seconds to a maximum of 120 seconds. If the 20 second
to 120 second ramp rate is not applicable to the particular installation, the ramp
rates may be changed by setting a miniature rocker switch. The switch is located
inside the cover on the printed circuit board, just to the right of the "ramp time
second" adjustment potentiometer.
The four switches on the mini-switch are numbered. Switches 1 and 2 control the
ramp times for the second ramp. Switches 3 and 4 set the ramp time for the first
ramp. The unit defaults to the first ramp, if the second ramp is not selected.
Approximate ramp times available are shown in the following table:
Ramp Time with Ramp Time with
Switch Location Adjustment Full CCW Adjustment Full CW
1st (default) Ramp
3 open 4 open 5 seconds to 25 seconds
3 open 4 closed 20 seconds to 120 seconds
3 closed 4 open 100 seconds to 10 minutes
2nd Ramp Selected
1 open 2 open 5 seconds to 25 seconds
1 open 2 closed 20 seconds to 120 seconds
1 closed 2 open 100 seconds to 10 minutes
Ramp time is the time it takes the output to ramp from the low limit to the high
limit and is independent of the values of the limits. The ramps are linear.
The time to ramp from the Low Limit to the Set Point is dependent on where the
Set Point is adjusted. If the Set Point is halfway between the low and high limits,
the ramp time will be one-half of the overall ramp time.
Plant Wiring
After the ramp rates have been selected, and the low limit, high limit, and
intermediate output positions are set, the reference unit should be permanently
wired into the electronic control loop.
Wire according to the plant-wiring diagram (Figure 3-1) and according to the
applications chart in Chapter 4. Observe the shielded wiring requirements
between the reference unit and the control system. All shields should terminate
at the control system only, not the reference unit. Do not terminate any shield at
both the reference unit and the control, as this will reduce the effectiveness of the
shield.
NOTE
The electronics of the Digital Reference Unit always respond to the lowest
signal selected, should two or more of the selection switches be closed at
the same time. The ramp will stop should a selection be opened before the
limit or set point has been reached.
When Set Point is selected, the output will ramp up or down as necessary to
reach the predetermined set point.
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