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The AUTO / MANUAL function allows you to manually adjust the output of the con-
trol. This is normally used during process setup or start up. It can also be used for
troubleshooting. To switch from AUTO to MANUAL press INDEX to Auto. Press the
UP ARROW to select OFF and press ENTER.The MANual indicator will light and the
lower display will change from normal to showing the actual output in percent. The
value will be the actual percentage of output that was active when the key was
pressed. This is usually known as "bumpless transfer".
If you wish to change the output while in manual, press the UP ARROW or DOWN
ARROW keys to change the value, and press ENTER to retain it. It is important to
remember that the value of the display can be read as 0 to100% of the full control
output, or 0 to 100% of the range between S1OL and S1OH or S2OL and S2OH. If
APct is set for rEAL, a reading of 50% in MANUAL represents 10 mA. If APCt is set
for AdJ, then 50% in MANUAL will represent the mid point in output between S1OL
and S1OH. (Assuming S1OL is 20 and S1OH is 100 [4 to 20 mA], 50% will repre-
sent 12 mA.)
To return to AUTOmatic control, press the ENTER until Auto is displayed. Press the
DOWN ARROW key to On, and press ENTER. The MANual indicator will go out, and
the set point will take over. If you want bumpless transfer back to AUTO, while in
manual, slowly change the percentage of output until the process variable matches
(or at least is close) to the set point.The further away the PV is from the set point, the
greater the "bump" or upset there will be in the output.
Self Tune®allows automatic selection of the necessary parameters to achieve best
control operation from your CN74000 Series control. If you are using the control out-
put as a simple on-off function (Out1 set for OnOF), none of the following will apply.
Theory of Operation
The Self Tune function calculates the Pb1, rES, and rtE parameters under the PID
tunE selection, and the Fbnd and FrtE parameters, as shown in the Secondary
Menu. These values are determined by measuring the response of the process con-
nected to the control. When Self Tune is started, the control temporarily acts as an
on-off control. While in this mode the control measures the overshoot and under-
shoot of the process, and the period of the process (the time from peak value to the
next peak value). These measurements are collected over a period that lasts three
periods of overshoot and undershoot.The data collected over this time is then com-
pared and calculated into final PID and Fuzzy Logic values. The effect of Fuzzy Logic
on the process is still controlled by the Fint (fuzzy intensity) setting. If Fint is 0, the
Fbnd and FrtE will be calculated, but will have no effect. The calculations for the
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