ATR 421 - User manual 21
Press Display Do
3
O
K
Green display shows the 
process. Red display shows 
P.---, where the output 
percentage value is visualized 
. Controller starts to modulate 
the command output.
To modify percentage pres 
 
or  . To esc press 
ST
A
R
T
STO
P
 for a 
second.
8  Programmer functions 
8.1  Hold function
This function allows to interrupt the cycle: red display visualizes   and cycle 
advancement is stopped. By pressing   and   it is also possible to mo-
dify the setpoint. 
There are two possibilities to start this function:
•  By keyboard: set En. on parameter 33 HLd.F.
 Press 
PRG
M
 for a second: function will be started or stopped.
•  By digital input: select HoLd on parameter 27 dGt.i. (only for ATR421-
14ABC). 
NB: It is not possible to enable Hold function by parameter 33 HLd .F if para-
meter 27 dGt.i. has already been set on HoLd. 
8.2  Automatic tuning 
Automatic tuning procedure has been conceived to give user the possibility 
to have a clear regulation also without knowledge of PID regulation algori-
thm. Setting Auto on parameter 11 tune, the controller will check process 
oscillations and will modify PID parameters if the di erence between process 
and setpoint values is greater than value on P-13 M.G. tu.
Parameters 13 M.G. tu, 14 M.n.P.b., 15 MA.P. b . and 16 Mn.i.t. can be modi-
 ed entering the dedicated  password 5678.