8
INTRODUCTION
Typographical conventions used in this manual
Glossary
Pay attention when you see these symbols in the manual.
Indicates very important information on correct
product function or on safety, or an instruction that
MUST be followed.
Indicates risk for the safety of the installer or user
due to the presence of high voltage.
Indicates a point to which the reader’s attention is
called.
Indicates a suggestion that could be useful for
better use of the device
Indicates a reference to other technical documents
that can be downloaded from www.gefran.com.
WWW
4...20 mA Current used as signal transmitted by
certain sensors or in a specific way to
control a device, such as a motorized
valve.
Alarm Output that trips when a certain condi-
tion is reached, for example, a defined
temperature
Auto Tune Function that lets you calculate and ea-
sily set the P, I and D parameters thanks
to the controller’s self-learning.
Cool Control used for cooling.
Heat/Cool Control used for both heating and coo-
ling (requires two control outputs).
Heat Control used for heating.
Hysteresis When, at a precise moment, the value of
the controlled quantity depends not only
on another reference quantity but also
on the values that the controlled quan-
tity had previously, there is hysteresis.
Hysteresis can therefore be considered
inertia that influences the control system,
causing variable delays between the
change of the reference quantity and the
change of the controlled quantity.
ON-OFF Control procedure based on activation
and deactivation of the output.
For heating, the output stays on until PV
is less than SV by a certain quantity (of-
fset), and then stays off until PV is not
greater than SV by the same quantity (or
different quantity, depending on control-
ler configuration).
For cooling, the output stays on until PV
> SV - offset and stays off until PV < SV
+ offset.
This type of control is not intelligent,
does not consider noise, and is not very
accurate, but ensures a limited number
of switchings of the output.
Overshoot Situation in which PV exceeds SV becau-
se the control action stopped too late.
The ON OFF controls have an overshoot
greater than the PID controls.
PID Acronym for Proportional-Integra-
tion-Differentiation, indicating a system
with negative feedback, i.e., a device
that acquires a value from a process in
input, compares it to a reference value,
and uses the difference (error) to calcu-
late the value of the controller output va-
riable, which is the variable that controls
the process.
The output is controlled based on the
current value of the error (proportional
action), on a set of previous error va-
lues (integral action), and on the speed
of change of the error value (derivative
action).
Pt100 A commonly used temperature measure-
ment device. At 0°C its resistance is 100
ohm, and at room temperature about
106 ohm. The Pt100 can be tested for
galvanic continuity and normal extension
cables can be used.
PV Acronym for Process Value, i.e., the value
that the process variable (temperature,
valve opening, etc.) has at that moment.
Solid state
relay
Also known as SSR, this is a relay desi-
gned specifically for frequent switching.
It has no moving parts or mechanical
contacts, but may still break or short cir-
cuit.
This type of relay is often used in tempe-
rature control systems such as PID.
Sensor Device that translates physical phe-
nomena (such as change in resistance
based on temperature) into electrical si-
gnals that can be acquired and proces-
sed by the controller
Setpoint Set value (see SV).
SV Acronym for Set Value, i.e., the value that
the process variable (temperature, valve
opening, etc.) has to reach and maintain.
Thermocouple Sensor that transmits an electrical signal
of a few millivolts. Cannot be tested for
galvanic continuity. It needs specially de-
signed extension cables
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