The S4 Group, Inc.

As our integration partners have been digging into some of the older Metasys® installations they are finding Generic IO / Point Multiplexor applications much more frequently than I thought they would. You can still do a very successful integration with these devices but it may take a bit more planning than if they were loaded with more traditional Metasys® applications.

The Generic IO / Point Multiplexor application turns the relatively smart Metasys® UNT or AHU devices into dumb I/O controllers. The yellow flag here is that if these points are utilized, the logic to drive them has to be coming from somewhere. Normally, this means that there is custom logic in the Metasys® supervisory controller. If you are planning on eliminating the current Metasys® head end you need to double your efforts to make sure that there is not any custom hosted there that you need to replace.

Sometimes, these devices have single side loops defined. These are small amounts of custom logic that can be defined in the AHU or UNT itself. Our custom Device Type Templates created by the Metasys® Configuration File Conversion Utility expose these points to you and you can work with them in your BACnet or OPC client just as you do any other point.

The risk to your customer at sites that have Generic IO / Point Multiplexor applications is that these installations are typically much more vulnerable to failures of the Metasys supervisory controller or the N2 bus when normal operation relies on custom logic in the supervisory controller. If the supervisory controller goes away unexpectedly the entire building goes down. As the earlier generation Metasys® supervisory controllers age this risk becomes higher.

There are several ways that we have found to address this condition:

1) Re-implement any logic that you find in the Metasys® supervisory controller utilizing a BACnet or OPC-based current generation controller.

2) Re-program the N2 device with a HVAC application appropriate for the task it is being asked to do utilizing the JCI HVAC Pro utility.

3) Replace this device with current technology controllers that have the capability to do the task required.

4) If the device contains single side loops and there is no custom logic in the Metasys® supervisory controller it can continue operating as it is.