37
Control Functions and Modes
The unit contains two relays, one for each limit. The relays are both connection relays, but the polarity
may be inverted independently using parameters no. 19 and 20 when in simple supervision and On/
Off control mode.
On/Off Control
When the measurement crosses the chosen setpoint, the relay will open and not close again until the
measurement exceeds the hysteresis band.
Hysteresis Band
A hysteresis band (a.k.a. dead band) always lies above a Min & below a Max limit. This is P17 for Limit 1
& P18 for Limit 2 in On/Off mode.
Proportional Band
The proportional band is a range where a variable control is performed. A proportion band lies above
a minimum and below a maximum limit. This is P17 for Limit 1 & P18 for Limit 2 in TPC control mode.
Basic Frequency
The basic frequencies for Limit 1 & 2 may be set from 1 to 250 pulse per minute (default 60). This is
valid in the PFC control mode only.
Proportional Frequency Control (PFC a.k.a. Variable Pulse)
If the measurement lies outside the proportional band the relay will pulsate with the basic frequency.
Inside the proportional band the frequency is changed linearly towards zero as the measurement
approaches the setpoint.
Time Proportional Control (TPC)
The time is constant and equal to the basic time. Instead the duty cycle is changed according to the
same principle as for PFC control. If the measurement lies outside the proportional band the relay is
closed permanently and open permanently if limit is exceeded.
Control examples
On/Off control may be used for alarms and simple control of pumps. Proportional frequency control is
primarily designed for the control of dosing pumps. Proportional time control may be used for control
where more fine approach is required than simple on/off control offers.
Parameters Accessible from LED Menu
In addition to the parameters in the setup menu, the FX-300-REL also features parameters directly
accessible from the main LED menu (see next column top). The parameters are accessible by pressing
the ‘Mode’ key until the LED for the parameter to be altered is lit. Use the ‘Up’ and ‘Down’ keys to alter
the parameter. These parameters and their functions are shown in the table below.
Par No. 01 is a
“lock” which must be ‘Off’ to change ANY parameter at all.
8 Additional Measurement & Function Modules
FX-300-REL Relay & Control
