====The Monitors Relationship====

This relationship is one of the most complex relationships in ARDI - this section discusses why you use it, and what it does.

**Monitors** is a [[logical relationships|logical relationship]] that is used to say 'Although this measurement is being taken //here//, it's actually measuring something located //elsewhere//.'

===Usage Example : Tank Monitoring===

A good example of this is tank monitoring. 

A tank may have several sensors hanging off it - for example, a level, temperature and pressure sensor.

Each of these are connected via a //fork// or //branch// in the relationship - they have their own piece of pipework with nothing else connected to it.

But although these measurements are being taken at points that are connected to the tank, the measurements themselves are really properties **of the tank itself**. To let ARDI know this, you connect the sensor to the tank via the **monitors** relationship.

===Usage Example : Temperature===

Another good example is in temperature monitoring.

After a heater or cooler, there may be a number of instruments (such as isolation valves, filters, flow meters etc.) between the item that changes the temperature, and the item that actually //monitors// that temperature.

Using the 'Monitors' relationship is a great way of telling ARDI where the temperature change actually takes place, ensuring that the information flowing through your relationships is accurate.

===The Effects===

When an asset has a [[parent|parent]] that //monitors// it, the parent asset is checked for properties.

Any measurements being made in the by the parent that either...

* Is present in both the parent and the child, or
 
* Can flow through the child based on a common [[physical relationships|physical relationship]]
   
...will be copied across, and work as if those measurements were being made at the child (for instance, values that are //monitored// this way still flow through your relationships, just as if they were being taken in the child asset itself).

===Why doesn't ARDI just copy ALL of the measurements?===

It's a good question.

The reason why ARDI doesn't copy //every// property from the parent to the child is that certain instruments record 'internal' information - details that are true only for the sensor, not for the item the sensor is monitoring.

For example, many pressure transmitters can also output their cell temperature. While this information might be useful for diagnostic purposes, the cell temperature of your pressure transmitter is often **not** the media temperature in the tank it is monitoring. This means that it shouldn't be copied as part of the Monitors relationship.

===How Do I Prevent A Property From Copying===

In some cases, there may actually be a property that is common to both items that you //don't// want copied between the assets.

This is often maintenance or construction information, such as 'Has this asset been installed' or 'Is an AR marker attached'.

In these cases, you can disable the use of the Monitors relationship by unchecking **Distribute Via Special Relationships** in the Options section when editing a property.

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