Head-mount transmitters are compact disc shaped transmitters most often mounted within a connection head which can be field mounted. Most common styles are DIN A and DIN B which differ slightly in dimensions and mounting method. However, the distance between the mounting screws is identical. See Figure
DIN A and DIN B Head-mount Housing Styles
These are commonly mounted in single compart- ment housings, such as sensor connection heads or junction boxes. Figure and Figure They can be mounted integrally with the sensor or remotely from the sensor. For integral mounting the transmitter housing is threaded directly onto the sensor / thermowell assembly. With the remote mount, the transmitter is installed within a housing on a pipe stand or other support in the vicinity of the sensor assembly.
Dual-compartment transmitter housings, often known as field mount, are a two part housing that isolates the transmitter electronics module from the terminal strip compartment to protect it from exposure to harsh plant environments. The terminal compartment contains the terminal and test connections for the sensor and signal wires and provides access to the terminal block for wiring and maintenance while isolating the transmitter electronics.
The electronic module with an optional display is in the second compartment. Any moisture / humidity or other contaminants that might find ingress into the housing through the conduit connections will be contained in the terminal section and not come in contact with the electronics thereby greatly reducing the risk of damage from environmental effects. Another benefit is the increased immunity of the electronics from EMI and RFI that may be conducted by the wiring
Dual compartment transmitters can be mounted directly on the sensor assembly or remotely on a pipe stand or other support in the vicinity of the sensor. Remote mounting may be necessary when the measurement point is inaccessible or when the process environment prevents the transmitter from being installed integrally with the sensor