Athena 2000 Series Panduan Pengoperasian - Halaman 10
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How to Set Reset, Proportional Band, and Rate
Optional 3 Mode
Auto reset action automatically, but slowly, corrects droop error in proportionally controlled processes. Ideal
(PID)
reset time is one half the period of oscillation of the process. Slower settings are safe, but sluggish. Faster
settings will cause continuous oscillation.
NOTE: : Each process
will tolerate differing
1.
warm-up curves.
Often, a fast warm-
up is more important
than the elimination
2.
of overshoot. If it is
important to eliminate
overshoot, a slower
3.
setting should be used,
but it will also add to
the time it takes the
process to reach the
4.
setpoint.
In general, it is
best to maintain the
5.
tightest parameters
possible (narrow
proportional band,
faster reset, faster rate)
that still deliver optimal
6.
process response.
7.
8.
9.
10.
11.
Maintenance
Some preventive maintenance steps on the controllers are:
1.
2.
10
For slow processes, move switches 1 and 2 off, set rate slow, proportional band wide, and go to
Step 4. Otherwise:
Set reset time (internal switches are indicated on automatic reset switch chart below). Use the
fastest time (0.8 minutes) for very fast processes, 1 minute for most others, as a first try.
Set the proportional band to full wide (270° clockwise). Make sure rate is full fast, turned full
clockwise, as well.)
Plug controller in, turn your process on.
Observe warm-up. If the process overshoots set- point and cycles in continually decreasing waves
until it finally stabilizes, the reset time is correct. Then proceed to Step 7. If it continues to oscillate,
reset it to short, continue with Step 6.
Set reset switches to the next slowest time. Repeat Step 5. Continue changing settings until the
process stabilizes.
Turn proportional band pot 1/4 turn toward nar- row (counterclockwise). Process could begin to
oscillate again. If it doesn't, proceed to step 8. If it oscillates, back up 1/8 turn clockwise.
Tighten proportional band by turning the pot counterclockwise. Observe the process. If oscillation
continues, widen back by 1/8 turn. Continue until the process stabilizes.
Set the rate. Rate action responds to sudden load changes and anticipates power output
requirements. It also helps to eliminate overshoot on start- up. Rate should be approximately
1/6 of reset time. If the reset time is 0.8 minutes, the rate should be turned clockwise. For 1
minute, mid-position. For 2 minutes, it should be at least 3/4 full; for 4 minutes full slow.
Turn the process off to cool, then start up again observing the warm-up curve. If it takes the
process too long to reach the setpoint, make the rate faster by turning it back clockwise. If, on the
other hand, it overshoots the setpoint by an amount that is not acceptable, slow the rate by turning
the pot counterclockwise.
Fine tuning. If, after having established parameters, you'd like to improve response, it can be
accomplished by a simple "trial and observation" technique.
A.
Change a parameter (either rate or proportional band) by a significant value (the pots
generally need to be moved 30° to produce an effect).
B.
Change the setpoint.
C.
Observe the way the process responds -- if response is improved (i.e., faster rise, less
overshoots, faster stabilization at setpoint), retain the new value. If not, return the
old value.
D.
Try another parameter.
Keep the controller fairly clean, and protect it from dirt, oil, and corrosion. An optional dust cover is
available for use in hostile environments.
Periodically recheck all electrical connections
Since the front panel and the meter face are plastic, do not use solvents to clean them.