FCM electronic regulator Cod. +302235300 - Rel. 2.0 del 30/11/98
8
• • Second probe management (not available in slave mode)
The value of the measurement actually used by the controller depends on the two probe inputs, and can be selected (parameter C19)
keeping into consideration the following elements:
• probe 1 (probe 2 not used);
• greater value of the two probes (lower in reverse operation);
• lower value of the two probes (greater in reverse operation);
• difference between the two probes (probe1 - probe2);
• probe 1 for control, probe 2 for defrost control.
• • Detection of disconnected probe
When using NTC or 4÷20 mA probes, their disconnection is automatically detected. In this case, a message will be displayed, the control
action will be interrupted and the 0÷10 V output will be disabled or forced to the set value (parameter C10). When the connection is
restored, control is automatically resumed. The detection of disconnected probes concerns exclusively the probes being currently used.
6.4 High and Low alarms (not available in slave mode)
If the measured value remains below the Low threshold (parameter P25) or above the High threshold (parameter P26) for a minimum
time defined by parameter P28, the dedicated alarm will be generated. A Low or High alarm condition results in the following signals:
• the buzzer sounds;
• a message appears on the display;
• energisation of the digital relay (if programmed);
• no effect on the control action.
Automatic disabling of the digital output can be programmed using parameter P27.
Fig.4
In the event of High alarm in “direct” mode or Low alarm in “reverse” mode:
the 0÷10 V output can be forced to its max. value (100%) irrespective of the maximum programmed value (parameter C10). The output
remains at 100% for the entire duration of the alarm. It is recommended, in this case, to set a low value for the alarm differential
(parameter P27), so that the alarm deactivates as soon as the controlled value returns within the alarm threshold.
6.5 Defrosting (not available in SLAVE mode)
When in cooling/heating operating mode with Defrost management (parameter C00=8), it is possible to set a Defrost threshold that
starts a defrost cycle (parameter P40). Below this threshold (with a delay defined by parameter P42):
• defrost starts;
• the relay output is commuted;
• control action interrupts;
• the 0÷10 V output is forced to the value fixed by parameter P45.
The Defrost procedure may last until the set Defrost threshold which makes the cycle end (parameter P41) has been exceeded:
1. if you set the max. allowable time (defined by parameter P43) Ü on exceeding the maximum time an alarm signal is generated. The
frequency of defrost cycles can be limited, by setting a minimum time between consecutive defrost cycles (parameter P44);
2. if you want to set a fixed time (parameter P43)
the threshold ending the defrost cycle must be set to its maximum value.
Defrost control:
• uses the same probes as those used for normal control functions, or
• uses probe 2 for Defrost control and probe 1 for normal control action.
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