5.2.14 Sensor Break, Loop Break, and Current (CT) Alarms
| P35 | Select P35 to configure Sensor Break Alarm Type. | ||
| on | A sensor fault will be detected (factory default). The alarm message S.br will be flashed in the display. An output attached to this alarm will operate as a logic OR with the alarm type also attached to the output. Acknowledging the alarm has no effect. | ||
| LAt | A sensor fault alarm will be latched. The alarm indication and the state of the output can only be acknowledged after the open circuit sensor condition has been repaired. Then, the output resets, the ALM beacon and the S.br indication disappear. Latching of the sensor break alarm is independent of any other alarm connected to the same output. | Note: In FM approved versions 816L, 808L and 804L Sensor Break Alarm is always latched. | |
| oFF | Open circuit sensor will not be detected. | ||
| P36 | Select P36 to configure Safe output power (sensor break). |
If a sensor break alarm occurs this parameter sets the output level that the controller will adopt. The default is 0% which means that all control outputs are off. The full range is limited by the settings of op.Lo and oP.Hi set in Level 2. These settings are also limited by P36. The level set must be chosen with care to make sure that the process does not over heat or over cool. It can, however, be useful to maintain a small amount of power to keep the process at a ‘standby’ temperature for a short time while the sensor is changed or the break is repaired.
The interaction between P36
and the output power limits
is illustrated in the sketch
 |
| P37 | Select P37 to configure Break alarms output | ||
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Break alarms include sensor break, loop break and current (CT) alarms. P37 attaches the break alarms to AL1, AL2 and/or AL3. AL1, AL2 and AL3 can only be selected if they have been connected to an output using P11 to P14. The selected output, which may be latched or unlatched, acts as a logic OR with other alarms attached to it. Note: A break alarm will still operate an output even if the alarm type is not configured, i.e. the alarm type may be set to nonE. |
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| none | The sensor break alarm is indication only and does not operate an output (factory default). | ||
| AL1 |
AL1, AL2, or AL3 must be connected to an output using ‘P’ codes P11, P12, P13 and/or P14, for it to become available in this list, otherwise it will not be shown here. If P37 is then configured for AL1, AL2, or AL3 the break alarm will operate on the appropriate output. |
Note: In FM approved versions 816L, 808L and 804L Sensor Break Alarm is always attached to AL2. | |
| AL2 | |||
| AL3 | |||
Note: It is possible to connect AL1 (or 2 or 3) to more than one output. In this case all outputs that have been connected will operate if AL1 (or 2 or 3) is active.
This is illustrated in the examples given in the table:
|
P11 OP1 |
P12 OP2 |
P13 OP3 |
P14 OP4 |
Alarms available in P37 |
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|
H |
C |
AL1 |
AL2 |
AL1 |
AL2 |
|
|
|
H |
AL1 |
AL2 |
AL3 |
AL1 |
AL2 |
AL3 |
|
|
AL1 |
AL2 |
AL3 |
none |
AL1 |
AL2 |
AL3 |
|
|
AL1 |
AL2 |
none |
none |
AL1 |
AL2 |
|
|
|
none |
none |
none |
none |
none |
none |
|
|
|
t.End |
t.run |
H |
none |
none |
none |
|
|
|
AL1 |
AL1 |
AL1 |
AL1 |
AL1 |
|
|
|
|
AL2 |
AL2 |
AL2 |
AL2 |
AL2 |
|
|
|
|
AL1 |
AL3 |
none |
none |
AL1 |
AL3 |
|
|
Example: To Configure a Sensor Break Alarm
This example is given for non FM approved controllers 816, 808 and 804 - the break alarms will be attached to AL1 which will operate the output 4 relay.
To connect alarm 1 to output 4, select P14 for AL1.
To attach the break alarms to alarm 1, select P37 for AL1.
If it is required to latch output 4, select P35 to latch the sensor break alarm, P33 to latch the load current alarms or P34 to latch the loop break alarm.
Select P36 and adjust to a value of output power which the controller should go to in the event of an open circuit sensor. This may be 0 or it may be a level which keeps the process in a ‘standby’ state. Care must be taken to ensure that the power level selected is safe for the process. In a temperature control application a separate over temperature unit should be used.
When the controller is in operating mode any break alarm will operate OP4. OP4 will also operate if AL1 type (P21) is configured.
|
Alarm |
Display |
|
Sensor break |
S.br |
|
Low load current threshold Ld.AL |
ct.Ld |
|
High leakage current threshold LE.AL |
ct.LE |
|
Loop break alarm |
L.br |
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Note: if AL1 Type = Hi (or D.hi or Bnd) then both S.br and AL1 will be flashed in the display because the sensor break alarm exceeds the high alarm setting. |
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