Dwyer 2600 - Manual (Page 18)

May, 2013 Page 18 of 52 949-1194 Rev. 7
AUTO / MANUAL OPERATION
The AUTO / MANUAL function allows you to manually adjust the output of the control. This
is normally used during process setup or start up. It can also be used for troubleshooting.
To switch from AUTO to MANUAL press the AUTO / MANUAL key and hold for three
seconds. 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 is read as 0 to 100% of the full control output, NOT
the range between S1OL and S1OH or S2OL and S2OH. For example, if the set point one
output is programmed for 4 to 20 mA (S1OL=20, S1OH=100), a reading of 50% in
MANUAL represents 10 mA, not 12 mA. This allows the operator to go above and below
the output range to allow for improperly function equipment that may be connected to the
control output.
To return to AUTOmatic control, press the AUTO / MANUAL key again. The MANual
indicator will go out, and the set point will take over. However, if you want bumpless
transfer back to AUTO, 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 FUNCTION
Self Tune allows automatic selection of the necessary parameters to achieve best control
operation from your 2600 Series control. If you are using the control output as a simple
on-off function (O u t 1 set for O n O F ), none of the following will apply.
Theory of Operation
The Self Tune function calculates the P b 1 , r E S , and r t E parameters under the P i d t u n E
selection, and the F b n d and F r t E parameters, as shown in the Secondary Menu. These
values are determined by measuring the response of the process connected 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 undershoot 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 compared and calculated into final
PID and Fuzzy Logic values. The effect of Fuzzy Logic on the process is still controlled by
the F i n t (fuzzy intensity) setting. If F i n t is 0 , the F b n d and F r t E will be calculated, but will
have no effect. The calculations for the PID values are the same as used in the standard
Ziegler - Nichols equations that have been recognized as standard for decades.
The only modification to the application of the Ziegler - Nichols equations is controlled by
the d F A C menu item. This menu item controls the amount of rate (derivative) that is
applied. A d F A C setting of 3 (factory default) or less allows for less damping. A d F A C
setting of 4 allows for critical damping as set forth in Ziegler - Nichols. A d F A C setting of 5
or more allows over damping of the process.