Metex 8760CLP Total Free Chlorine & pH Analyzer User Manual
Page 52
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52
High or Low Alarm
A high alarm is set when the value of the chlorine, pH or temperature rises above the set-point and is
cleared when that value drops to below the set-point minus the differential (refer to illustration 41). A
low alarm is set when the value of the chlorine, pH or temperature drops below the set-point and is
cleared when that value rises to above the set-point plus the differential (refer to illustration 42). The
differential has the effect of setting the sensitivity of the alarm. The differential provides a digital
equivalent of a hysteresis.
A two-stage alarm can be implemented by choosing the same alarm function, ie. high or low alarm, for
both alarms, but selecting different set-points.
Example:
The HOCl of a critical process may not drop to below 0.5 ppm. Use alarm A as a low alarm set at
0.5 ppm and use alarm B as an advance warning device by configuring it as a low alarm set at 0.75 ppm.
When alarm B is activated there is still time left to take corrective action.
Deviation Alarm
A deviation alarm is practical when the process is expected to stay within a certain range. An alarm will
be set if the input deviates too far from a set-point. Note that the [dEv] frame only shows up in the
menu after the alarm function has been changed to deviation alarm; it would have no effect for a high,
low, or fault alarm.
Example:
If the total free chlorine concentration is expected to stay between 0.2 ppm and 1.0 ppm, then we would
set [in] to [tFCl], [Func] to [dEv], [SEt] to 0.6, and [dEv] to 0.4. Effectively, a high alarm at 1.0 ppm
and a low alarm at 0.2 ppm has been set.
The differential setting will continue to function as for high and low alarms.
Illustration 42: Low alarm
Illustration 41: High alarm