System Operation:

Automatic Calibration

Alarm Priorities

Normal Monitoring Function

Detail Operation of the EWS Monitor Panel


Automatic Calibration:

After installation of the Sensors, a 24 hour calibration period is started. There are several installer-settable options for each input channel and alarm function. These are typically set up by the installer to be appropriate for the system being monitored. The installer needs to be sure that the system being monitored is "normal" at the time of calibration. During the calibration period, the microprocessor in the Monitor Panel keeps track of when the motor starts and stops, the peak current during starting of the motor, and the motor running current. The monitor will consider the conditions over the next 24 hours as "normal" and will base alarms on those values. Certain settings such as the alarm threshold can be changed after calibration. Usually, after the calibration sequence is started, the installer can leave the site.

When the calibration period is complete, the Monitor System knows:

-  which sensor inputs are being used,

-  the typical running time of the motor (Duty Cycle),

-  the typical running current (ON current),

-  the peak current to expect during starting of the load,

-  the minimum current to expect for detection of a circuit breaker trip, and

-  the average process temperature

After the 24 hour calibration period is complete, the monitor system goes into a continuous monitoring mode watching for:

-  process temperature changes,

-  a circuit breaker trip,

-  load starting currents that are too high,

-  operating currents that are too high or too low,

-  duty cycle of the load that is too high or too low, and

-  an open circuit in the switch monitor loop.

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Normal Monitoring Function:

After calibration all channels that had valid sensor signals during calibration will come on with a Green (GRN) indicator ON. Any unused inputs have both the RED and GRN indicator OFF.

If an abnormal condition is detected, then an audio alarm is generated and a RED indicator is turned ON blinking to show which channel has a problem and a RED indicator shows what type of alarm condition was detected. By observing the alarm and channel indicators, it is easy to see what has caused the alarm.

The audio alarm is silenced by pressing a switch on the front of the Monitor Panel. When an alarm condition is acknowledged, the blinking RED indicator will stay on solid RED as long as the problem persists. If the problem is corrected, then the RED indicator will turn OFF and the GRN indicator will turn back ON.

There is a delay between when the local audio alarm on the EWS-MP sounds and when the alarm circuit output is created. (The delay can be set to 5 minutes or 1 hour) This is to allow the operator to correct the problem before an alarm is called out to a monitoring station (if the MP is connected to a remote alarm monitoring service).

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Alarm Priorities:

Since the usual purpose of a mechanical system is to provide control of a process temperature, the most serious condition is that the temperature is out of range. The sensor temperature is averaged for about 10 seconds and if the temperature goes out of range, an alarm will be generated within 20 seconds.

If a circuit breaker trips and power is no longer available to the load, soon the process will not be correct. A circuit breaker trip will be detected within 2 minutes. Typically, a pilot light or control transformer is adequate minimum load to monitor for circuit breaker tripping. For 3-phase loads, current in all three phases must be zero before a breaker trip is detected. For single phase loads, each circuit is processed individually for breaker tripping.

If the switch contact circuit is left open continuously for more than 5 minutes, then the switch monitor alarm will be generated.

There are three alarm conditions that make sense only if based on a 24 hour period. If excessive load starting current is detected, if the average current during running is out of range, or if the load duty cycle (ratio of ON to OFF time) is out of range over a 24 hour period, then the 24 hour function alarm will be generated.

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Detail Operation of the EWS-MP Monitor Panel:

Current Monitoring:

Running current is measured 1000 times per second and is averaged over one-minute intervals to see if the motor is ON or OFF. The ON current is averaged for 24 hours and compared to the average ON current during calibration. Abnormal running current is detected when the operating current signal is outside of the limits allowed. There are 3 user-selectable ranges (in addition to OFF) of the limits for operating current. The installer will choose a limit range that is appropriate for the type of load to minimize false alarms.

The ratio of ON time to OFF time is the load duty cycle. During each subsequent 24 hour period, the duty cycle is calculated and a duty cycle error is reported if it is outside of the limits allowed. Some loads are ON all the time or are so variable that duty cycle alarms would occur too often. The installer can enable or disable the duty cycle alarm function to minimize false alarms for certain applications.

The peak current (that usually occurs during starting of a motor load) is monitored and a counter measures the time duration that the current has exceeded the peak current found during calibration. The peak current threshold is related to the limit range set for the average running current. At the end of a 24 hour period, if the counter has found excessive peak current, then an alarm is generated. The installer can disable the peak current alarm function to minimize false alarms for certain applications.

Temperature Monitoring:

A second function of the EWS-MP is temperature monitoring. In a refrigeration system, even if abnormal operation was not detected by looking at the motor currents, there is backup monitoring of the temperature of the conditioned space. During calibration, the average temperature of the sensor in the space or product is monitored to establish a setpoint value. After calibration, the sensor temperature is averaged over a 10 second interval and compared to the setpoint. If the temperature exceeds the limits selected, (either too hot or too cold) then an alarm is generated. The installer can select 4 ranges of temperature limits to suit the application.

Switch Signal Timer:

A third function of the EWS-MP is to monitor a switch signal input. Walk-in freezers and product display cases with doors can have extreme variations in temperature if the doors are left open too long. By installing door switches on these doors and connecting them to the monitored switch input, if a door is left open continuously for more than 5 minutes, then an alarm is generated.

Indicators show Good and Bad:

The Monitor Panel has LED indicators to show which channels are active, which are operating normally, and which have been detected with a fault. If no sensor is detected during calibration, then both LEDs associated with that channel are OFF. If a channel is operating normally, then a Green LED is ON. When a fault is detected, the Green normal LED goes OFF and the Red LED comes ON blinking.

The type of fault detected is shown by one of 4 Alarm condition LEDs and the local audio alarm comes ON. If an optional remote alarm is installed, then it also will beep. If someone is on the site to hear the alarms, they can go to the panel to see what is indicated and press the Alarm acknowledge switch on the panel. The audio alarm will silence, and the Red blinking LED will stay Red will stay ON until the problem is corrected. When the problem is corrected, the Red LED will go OFF and the Green LED will come back ON.

If a temperature alarm condition is detected and the Red LED comes on blinking but the problem goes away by itself before an operator gets back to the panel to acknowledge the problem, the Red LED will still be blinking and the Green LED will also be ON to show that the present condition is normal.

If a switch input alarm condition is detected and the problem is corrected before the operator gets back to the panel to acknowledge the problem, the Red LED turns OFF and the Green LED comes back ON, and the local audio alarm turns itself OFF. This feature allows the operator to fix the problem and not have to go back to the Monitor Panel to acknowledge the alarm.

If the alarm is not acknowledged for 5 minutes then the remote alarm signal is activated. If the Monitor Panel is connected to a security system dialer, then the security monitoring service will be called with the alarm. The installer can select a 1 hour delay instead of the standard 5 minute delay before call-out. If the problem is fixed before the call-out delay has expired, then the call-out is reset.

For example, if the switch input circuit is open for more than 5 minutes, then the alarm will be initiated, the audio alarm will sound, the Green indicator will go OFF the Red indicator will come ON blinking, and the remote call-out delay timer will start counting down. As soon as the circuit is closed again, the alarm will be acknowledged, the indicator will go back to Green, the audio alarm will silence, and the remote alarm call-out will be abandoned. If the switch signal input is used to monitor freezer display cabinet doors, and the alarm comes ON because the 5 minute interval has expired, then the alarm condition can be acknowledged and reset by closing the door.

If an alarm was acknowledged (a Red indicator is ON continuously) at the site but the problem was not corrected before the 24 hour period expired, then the alarm will be re-asserted to remind the operator. (The reminder alarm is generated on the 24 hour anniversary of the initiation of a calibration cycle, not 24 hours from when the alarm occurred.)

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