991 Vibration Transmitter Introduction

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 occurs.

The 991 transmitter provides the following notable features:

1. Integrated Proximitor Sensor requires no external unit

2. Non-isolated "PROX OUT " and "COM" terminals plus a coaxial connector provide a dynamic vibration and gap voltage signal output for diagnostics3.

3. Non-interacting zero and span potentiometers under the Transmitter label supports loop adjustment.

4. Test Input pin allows quick verification of loop signal output, using a variable DC voltage source as the input.

5. A Power-up Inhibit circuit eliminates signal errors due to line voltage transients.

6. A Not OK/Signal Defeat circuit prevents high outputs or false alarms due to a faulty proximity probe or loose connection.

7. Choice of DIN-rail clips or bulkhead mounting screws as standard options simplifies mounting.

8. Potted construction for high humidity (up to 100% condensing) environments.

9. Compatibility with 3300 NSv proximity probe allows transducer installation in small areas with minimal