There are times that an alarm can’t be removed or an alarm set point can’t be changed to resolve a noisy process signal causing a chattering alarm. When this occurs, there are techniques that can be applied to the process signal or alarm to reduce alarm chattering. It’s important to understand the effect each method will have on the alarm or process measurement prior to implementing it. This article discusses each technique and the results when applied.
These techniques should never be applied blindly because they’ll likely not have the positive impact that was desired and could cause measurement issues or mask an alarm or delay a response by the operator. Before considering which method to apply, the reason(s) for false positive alarms must be determined for all states of the operation (startup, trip, normal, etc.). Solving the alarm issue for one operating condition may mask an alarm that’s real in another condition. Once the issues have been defined, then consider which technique will solve most of the false alarms.
A frequent mistake is increasing the masking effect because the applied technique did not resolve most of the false positive alarms. An example of this would be to increase the delay time from five seconds to five minutes. This will reduce more false positive alarms, but can lead to masking real alarms by delaying activation of the alarm until the five-minute delay has expired. The correct solution may be to apply a different technique or apply more than one technique to get the desired result of reduced false-positive alarms and minimized masking of real alarms.
Read the full story on controlglobal.com.