L-VIS User Manual 161 LOYTEC
Version 6.2 LOYTEC electronics GmbH
turn it back on until the device significantly cooled down, to avoid constant ON/OFF
cycles.
Such an application can be done by connecting the temperature data point two times. To
distinguish between them, append SET to the name of the first data point and CLEAR to
the name of the second data point (on the General property page).
On the Alarm Generator property page, configure the SET data point to cause the Action
‘set on alarm enter’, enter T1 as the maximum value of the Data Point Value Range, and
select Above Max for the alarm condition. For the Alarm Output, choose the desired output
value for the Set Action. The Clear Action should be grayed out, since the rule specifies no
alarm clear action.
Now there are two options available to configure the CLEAR data point. Here is the first
one:
Like on the SET data point, keep the Alarm Condition at Above Max, but enter T2 as the
maximum, instead of T1. For the Action, select Clear on Alarm Leave and select the desired
output value from the dropdown list at the right. This time, the Value for Alarm Clear box
will be active, while the others will be grayed out.
This method is the correct way of doing it, but it may be counter-intuitive. Many people
choose Below Min. for the alarm condition, because they want something to happen when
the temperature falls below T2. However, the condition specified here is always the Alarm
Condition. It defines the conditions under which the alarm is considered to be SET. It does
not define when something will happen. This is done using the Action setting. The alarm
condition in this example is still ‘above a certain temperature’ and action will be taken
when this alarm condition is CLEARED, e.g. the device has cooled down enough. Now, if
this seems unreasonable, here is an alternative approach:
You may configure the CLEAR data point using the alarm condition Below Min. and enter
T2 as the minimum value of the Data Point Value Range. Since you now defined ‘below
T2’ as the alarm condition, you need to take action when the alarm is SET, so the action
must be Set on Alarm Enter. Now select the desired output value from the Value for Alarm
Set Action dropdown list. This value will represent the cleared alarm, since the temperature
now is below T2. Overall, this way seems more awkward than the first, because the alarm
output is cleared by causing an alarm condition.
9.11.2.2 Alarm Clear via Data Point
Similar to the first example, but instead of defining a temperature T2 below which the
alarm will clear automatically, a manual input should be used to clear the alarm. Of course,
the two examples may be combined to have both, automatic clearance below a safe
temperature T2 plus manual clearance as long as the temperature is at least below T1.
First, we need to connect the input data point, via which the alarm should be clearable. This
may be the state component of a switch, a Boolean value, a register, or any other scalar
value. We will assume an internal register for this example, which we assume will be set by
the user pressing a button on the display. We assume that pressing the button will set the
register from 0 to 1 and releasing the button will set it back to 0 again.
The first part is the same as in the previous example. The temperature variable is connected
to the alarm generator and configured to cause an alarm when the temperature rises above
T1.
To clear this alarm, we configure the connected register data point as follows:
Set the Alarm Condition to Above Max. and enter a time delay of for example 3s. This will
require the user to press and hold the button for 3 seconds, before the alarm will be cleared.
Enter a value between 0 and 1 for the maximum of the data point value range, for example
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