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PRESYS
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Instruments
When the remote setpoint is enabled, the lower and upper displays will only
indicate the values associated to the control loop 1 and the UP and DOWN keys will
not actuate on the setpoint value shown on the lower display, since it is being
externally controlled.
STATUS - this is the option which actually enables (ON) or disables (OFF) the
remote setpoint. This is an option which allows a quick changeover between a local
and a remote setpoint.
Input 2 on the Controllers, receiving the remote setpoint signal, is adjusted to
the span of input 1 in terms of engineering units by means of the RATE and BIAS
parameters, according with the equation shown below:
RATE, BIAS - gain and offset adjusting the span of input 2, in engineering
units, to the span, in engineering units of input 1.
CASCADE - this type of control is used for a process in which the controlled
variable is affected by several other rapidly varying external variables, but whose
effects would be shown with great delay in the controlled variable. This type of control
uses two Controllers. For the DCY-2057 Controller, control block 1 will act as the
master Controller and its output will provide the slave Controller with the setpoint
which will be the control block 2, as illustrated on figure 23, below.
INPUT 1
INPUT 2
Fig. 23 - Conceptual block diagram of the control blocks and
In the case of the cascade control indicating the values of the controlled
variable (upper display) and the setpoint/output (lower display) for control block 2
(slave Controller) the UP and DOWN keys will not actuate on the setpoint value
shown on the lower display, since it is controlled by the output of control block 1
(master Controller).
CTRL1, CTRL2 - represent control blocks 1 and 2; they may be associated
with the various control modes described below. CTRL2 is presented only when
channel 2 is enabled.
DCY - 2057 Pressure Controller
SP.RE = RATE * (Input 2) + BIAS
SP1
SP2
display for the cascade control
OUT1
OUT2
Maintenance
Page 37
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