The 991 Thrust Transmitter is intended primarily for the original equipment
manufacturers (OEMs) of centrifugal air compressors or small pumps, motors, or fans who prefer to provide a simple 4 to 20 mA proportional axial displacement (thrust) signal as the input to their machinery control system. The transmitter is a 2-wire, loop-powered device that accepts input from our 3300 NSv* proximity probe and its matching extension cable (available in 5 m and 7 m system length options). The transmitter conditions the signal into appropriate engineering units proportional to the shaft’s axial position1, and provides it as a 4 to 20 mA industry-standard signal for input to the control system where machinery protection alarming and logic occurs2.
The 991 transmitter provides the following notable features:
 Integrated Proximitor* Sensor requires no external unit
 Non-isolated “PROX OUT " and "COM" terminals plus a coaxial connector provide a dynamic vibration and gap voltage signal output for diagnostics3.
 Non-interacting zero and span potentiometers under the Transmitter label supports loop adjustment.
 Test Input pin allows quick verification of loop signal output, using a variable DC voltage source as the input.
 A Power-up Inhibit circuit eliminates signal errors due to line voltage transients.
 A Not OK/Signal Defeat circuit prevents high outputs or false alarms due to a faulty proximity probe or loose connection.
 Choice of DIN-rail clips or bulkhead mounting screws as standard options simplifies mounting.
 Potted construction for high humidity (up to 100% condensing) environments.
 Compatibility with 3300 NSv proximity probe allows transducer installation in small areas with minimal clearance, typical of centrifugal air compressors.