Pid Variable Configuration - gefran 3850T Use And Installation Manual

• low on: current absorption value under which the HP
alarm triggers when the control output is ON.
• hig on: current absorption value over which the HP
alarm triggers when the control output is ON.
• time: minimum time when exceeding LOW_ON, HIG_
ON and HI_OFF must be valid before the HB alarm
triggers.
• hig off: current absorption value over which the HP
alarm triggers when the control output is OFF.
• AL: lets you associated an alarm to HB alarm detec-
tion.
• OUT: lets you associate any digital variable (except
input digital variables) to the HB signal.
Management of HB alarms
Single-phase load: there is only one current signal, so its
management is simple. Simply enter the security band for
ON current and the maximum limit for OFF current. Take
into consideration that not only a failure (or deterioration) of
loads can cause a variation in current, but also oscillation
of line voltage. You should therefore set thresholds with a
certain amount of margin, capable of "tolerating" oscillation
in the power supply.
Three-phase load:
With a three-phase system you will need to set 2 TAs.
Let us consider the case of a symmetrical, balanced three-
phase system with balanced loads.
CASE 1) closed triangle load, a failure in a resistance
(open circuit) generates a drop of about 42% in current on
other branches. So if there is a failure, at least one CT will
show a drop in current of about 42%.
CASE 2) load is star without neutral, a failure in a resis-
tance generates total absence of current on the phase
connected with the faulty resistance, and a drop of about
13% in the other two phases.
And so in case 1, the variation in current will be easy to see
with good sensitivity in at least one TA. Even if the system
is not ratiometric with line voltage, its nominal fluctuation
(+10%/-10%) will NOT create false alarms. In conclusion,
the breakage of a resistance is always detected by setting
the threshold LOW_ON>58%. This means we can prac-
tically reach 70% (with no risk of false alarms due to line
variations).
In case 2, seeing as the CT may not be connected to the
faulty line (where the fault is evident), it will be necessary
to tighten the alarm threshold and set LOW_ON>87%. As
the system is not ratiometric with line voltage, fluctuation
of (+10%/-10%) can result in false alarms. It is therefore
suggested that you set the value of LOW_ON to 90% (with
a slight risk of false alarm due to the line if it drops by 10%).
To ensure secure interception of the failure under any con-
ditions, independently of changes in voltage, use of 3 TAs
will be necessary,
Through logical functions and the available CT variables (if
the system configuration has at least 3 TAs), you can check
that each line does not go down to zero (a clear fault condi-
tion). In this way you are immune to line oscillation.
For variable names, the list can be scrolled using the but-
tons on the right of the display:
and move the list by 3 variables;
80703B_MHW_2850T/3850T_02-2019_ENG
and move the list by 10 variables;
You can also jump directly to specific points in the list by
touching the alphabetic directory keys. When the key is
marked with two characters or digits (for example, A0, B1,
etc.) quickly touch the key twice to jump to the second
character. The sp button means "space".
Once you see the variable, touch it to select it.
The CLEAR button deletes any variable in the field and
closes the window; the field becomes empty.
Touching the X at the top right corner closes the window
without confirming any selections.
Power displays the percent power calculated at that time
by the PID and if used for heating (red LED) or cooling (blue
LED).

4.15.4.9. PID variable configuration

The Variable section lets you associate variables to PID
inputs and outputs.
The displayed screen depends on the PID operating mode,
that is set in the Synoptic section.
Normal PID
Cascade PID
4. CONFIGURATION
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