Operation of BMS Lockout Indication
Radiant tube heaters can have an option of Lockout Indication if the burner fails to light on start up. This usually takes the form of a volt free circuit which is connected to two additional connections mounted on the burner housing. These connections are volt free and can form either a Normally Open or Normally Closed circuit depending on the customers requirement and connections made.
To allow correct lockout indication the following conditions at the BMS must be observed.
Any software or circuitry must be programmed to request a lockout condition only when the system is calling for heat.
In addition, it should also provide a 60 second delay before indicating lockout. This is to allow the sequence controller to operate after the initial supply is connected to the heater when calling for heat via the control system and any restart attempt if necessary.
Note: If the above points are not complied with the BMS will receive a false report of the burner status.
Drawings attached show typical BMS lockout schematics for Nor-Ray-Vac radiant systems.