How to Calculate How Many Alarm Points to Monitor

At first glance, a survey of your remote site might show that you need to monitor a few basic environmental alarms or a few pieces of equipment. So you may think that you're looking for a system that can monitor 6 alarm points. But is that enough?

Let's examine elements of remote sites that require monitoring. Identifying these elements will help you plan your remote site monitoring needs. Also, it will help you choose the right RTU for your specific needs.

Discrete Alarms

Contact closures are known as alarm inputs, discrete alarms, or digital inputs. Discrete alarm points are those which can be measured in terms of "On/Off", "Opened/Closed" or "Yes/No".

NetGuardian 832A G5 Back Panel
The back panel of the the NetGuardian 832A G5 features ports for discrete and analog inputs, which allow you to remotely monitor up to 32 discrete points and 8 analogs. Expansion units can be daisy-chained to the device to add additional capacity.

Here are items that are commonly monitored as discrete alarms:

Using SNMP environmental alarm monitoring is a common method to keep an eye on environmental conditions at your facility.

Analog Alarms

Analog alarm inputs typically measure a range of values, unlike on/off discrete alarms. A common example of an analog application is the measurement of temperature.

If you have analog alarm values to measure, you need to define the thresholds at which your monitoring system will take action.

For example, suppose you are measuring the temperature of a remote site. Building temperatures range from 10 to 120 degrees Fahrenheit. Under normal conditions, the building's heating and cooling system will keep the temperature within an acceptable range. To take advantage of multiple analog values, you might set up 4 different threshold values like below:

  1. When the temperature is below 30 degrees, page a technician and notify the Network Operations Center (NOC). A value this low might indicate that the heater is not working at all.
  2. When the temperature is below 50 degrees, notify the NOC. This may indicate that the heater is not functioning properly.
  3. When the temperature is above 80 degrees, notify the NOC. This may indicate that the air conditioning unit is not functioning properly.
  4. When the temperature is above 100 degrees, page a technician, notify the NOC and open a vent (via derived controls). This may indicate that the air conditioning unit is not functioning at all.

Note: To gain this level of detailed visibility, be sure to look for a monitoring system that can accept at least four separate analog threshold values.

Craft Ports

You may have devices such as PBXs, routers, and switches at your remote site that need setting up, also referred to as provisioning. Normally, this would involve driving to the sight, setting up a laptop, and creating a terminal session through the device's "Craft Port" (typically a serial port-"craft" is a reference to the craft personnel who work with telemetry devices).

You may also need to manage streaming ASCII data from one of these devices. Often, ASCII data is sent to a serial printer port either to be printed or captured into a database.

In both of these cases, a remote solution is ideal. Make sure that if you do have such devices and applications, you look for the following features in a remote monitoring system:

  1. It should function as a pass-through terminal server that gives access to remote craft ports. Be sure to consider how many ports you are going to need access to when selecting your monitoring solution and allow for expansion.
  2. It should have multiple access methods (for example, LAN and dial-up). It is best practice to have a secondary connection in case the primary connection should fail.
  3. It should be able to serve as a proxy to other network elements in order to capture ASCII data.

Note: Be sure to allow some room for expansion. Once you discover the advantages of a remote terminal server, you're sure to find more applications, which will require more serial ports.

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