Before describing how to program the instrument, it is necessary to review some basic
concepts:
- Direct Mode and Reverse Mode: a regulator works in Direct mode
, when it tends to
operate against the rise of the controlled variable. Direct function is typical, for example,
of refrigeration: the more the measured temperature increases the more the capacity of
the refrigeration circuit increases, so as to make temperature itself fall.We use the term
Re
verse if the regulation tends to operate against the decreasing of the controlled
variable.This is used, for example, in heating systems where you have to oppose the
decreasing temperature by increasing the heat production.
- Set-point (or Set): this is the value that the controlled parameter has to maintain, for
example the value of the temperature at which an oven is to work.When the controlled
parameter is at the Set-point value, all outputs are de-activated.
- Differential or hysteresis: regulates the outputs when the controlled parameter
deviates from the Set.Without Differential the instrument could pass suddenly from all
outputs OFF (parameter equal to SET) to all outputs ON (parameter different from SET).
Instead, when differential > 0, the outputs insertion is gradual and the regulator will
activate all outputs only when the difference between the controlled parameter and the
Set Point exceeds the value of the Differential. A ‘narrow’ differential usually maintains the
controlled parameter very near to the Set, but it can provoke frequent turning ON and
OFF of the controlled devices i.e. hunting problems.If a very precise regulation is
required, instead of selecting a narrow differential, the P+I regulation (described in the
“Technial Manual”) can be activated.
39
Easy set-up: basic concepts
+05-3015 • rel.3.0 interno ok 18-09-2002 14:31 Pagina 39
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