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the output operating in the retransmission mode enables the conversion of the input signal to the output signal
(in the range ArLo ÷ ArHi ). In the control output mode, the control parameters and functions are the same as for
the related output 1/2/3, but the variability range of the analog signal is continuous (0 ÷ 100%) only for the PID
algorithm (chapter 9.3) and manual operation, for the control of ON-OFF type with hysteresis, the output has
extreme values (bottom or upper value, e.g. 0mA = 0% = OFF or 20mA = 100% = ON) without intermediate values,
which can be used e.g. to activate the SSR relay.
The values of the output signal (mA/V) can be presented in the form of a bargraph on the bottom line of the
display (parameter 73: dibo = bArA) or read from the level of MODBUS-RTU/TCP and MQTT protocols, chapter 11.
Moreover, it is possible to correct (calibrate) the range of changes of the output signal (parameters 34: cbot and
35: ctoP).
9.3. PID CONTROL
The PID algorithm makes it possible to obtain smaller temperature
control errors than the ON-OFF method with hysteresis. However,
this algorithm requires selection of parameters characteristic for a
specific regulation object (eg a furnace). In order to simplify the
handling, the controller is equipped with advanced functions of PID
parameter selection, described in chapter 9.4. In addition, it is always
possible to manually adjust the settings (chapter 9.5).
The PID control for a given control output is active when one of the
three sets of PID parameters is selected (with the parameter
ctY1/2/3 , description in chapter 8, Table 8, point II, or with the
parameter PSE1/2/3, point V), i.e. PiD1/2/3.
The position of the proportional band Pb (Pb1/2/3, Table 8, point IV)
in relation to the setpoint SP (SEt1/2/3) is shown in Figures 9.3 a)
and b). The parameters ti1/2/3and td1/2/3 are responsible for the
influence of the integral and derivative element of the PID control.
The parameter PEr1/2/3 sets the pulse period Tc for the P/SSR
output (it is also the time of its status update), while oPF1/2/3 the
available power used for selecting PID parameters. If the PID
algorithm is implemented by the 0/4 ÷ 20mA or 0/2 ÷ 10V analog
output, the Tc period is irrelevant. The mA/V output signal is then
updated every 1 s and it can adopt intermediate values from the
entire range of output variability (0÷100%).
The principle of operation of the P-type control (proportional
control) for the P/SSR output is shown in figures d), e) for the analog
output, figure c).
Fig. 9.3. Principle of PID regulation operation:
a) position of the Pb proportional band in relation to the setpoint SP
for the heating type control (Fvn1/2/3 = indH )
b) position of the proportional band Pb in relation to the setpoint SP
for the cooling type control (Fvn1/2/3 = dirC)
c) the status of the analog output 0/4÷20 mA or 0/2÷10V
d) duty factor k for a bi-state P/SSR output
e) the status of the output for the measured value PV within the Pb
range
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