Bently Nevada 3500/72M Recip Rod Position Monitor

Overview

The Bently Nevada 3500/72M Recip Rod Position Monitor is a four-channel module for the Bently Nevada 3500 rack that accepts proximity transducer signals from the piston rods of reciprocating compressors. It conditions each signal into dynamic and static position measurements and compares them with user-programmable alarms, so that rider band wear, crosshead problems and rod flexing are seen while they can still be managed. The Bently Nevada 3500/72M meets API 618 requirements for reciprocating compressors and supports three families of measurement: rod position, rod drop and hyper-compressor monitoring.

Seven Star LLC supplies the Bently Nevada 3500/72M, its I/O modules and the related external termination blocks and cables to compressor operators in the Sultanate of Oman and neighbouring GCC states, backed by regionally held stock and application help from our engineers in Muscat. Datasheet 146478 Rev. M is attached below, and we can check rack software versions and I/O choices with you before you order.

Measurement Principle

A proximity probe mounted near the packing case looks at the piston rod and measures the gap between probe tip and rod. As the rider bands on a horizontal piston wear, the piston settles and the rod drops toward the probe. In Rod Drop mode the Bently Nevada 3500/72M reports average piston position, average probe gap, instantaneous piston position and instantaneous probe gap, which together tell the operator how much rider band material remains. In Rod Position mode, used singly or with two probes at 90° as a pair, the module returns position magnitude, position angle, crank angle, peak-to-peak amplitude, gap, 1X, 2X and Not 1X amplitude, describing how the rod moves through each revolution.

The Rod Position 2 channel types add average and instantaneous piston position, and the Hyper channel type serves hyper-compressors such as those in low-density polyethylene plants, returning peak-to-peak displacement, gap and 1X, 2X and Not 1X amplitudes. Peak-to-peak filters are fixed at 1 to 600 Hz and gap filters are −3 dB at 0.09 Hz. The 1X and 2X vector and Not 1X values are valid between 60 and 2130 cpm, and the Not 1X notch rejects at least 34.9 dB from 60 cpm to 15.8 times running speed. Magnitudes are accurate within ±0.33% of full scale typical (±1% maximum) and angles within ±1° typical (±3° maximum).

Engineering Design of the Bently Nevada 3500/72M

The Bently Nevada 3500/72M needs a single full-height slot at the front of the rack plus a matching rear I/O slot. Its 10 kΩ inputs accept one to four proximity probe signals and supply them with −24 Vdc transducer power. Nominal scale factors are 0.79 mV/µm (20 mV/mil), 3.94 mV/µm (100 mV/mil) or 7.87 mV/µm (200 mV/mil) for rod position, and 100 or 200 mV/mil for the other channel types. The front panel carries OK, TX/RX and Bypass LEDs plus a coaxial buffered output for every channel (510 Ω, protected against short circuits). Power consumption is 7.7 W nominal and the main board weighs 0.91 kg.

Channels are programmed in pairs and can perform up to two functions at a time, for example rod drop on channels 1 and 2 and rod position on channels 3 and 4. Alert setpoints can be applied to each measured value and Danger setpoints to any two, with Danger delays of 0.1 second nominal or 1 to 60 seconds. Timed OK channel defeat is disabled for rod position and rod drop configurations, and in hyper-compressor service the monitor issues a Danger alarm immediately when both transducers are not OK. The standard product works down to 60 rpm; modification 135M8199-01 extends this to 30 rpm.

Key Features

According to its datasheet, the Bently Nevada 3500/72M offers:

• Four proximity probe channels for rod position, rod drop and hyper-compressor measurements.
• Compliance with API 618 requirements for reciprocating compressor rod monitoring.
• Rod drop values for average and instantaneous piston position and probe gap.
• Rod position values including position magnitude, position angle and crank angle.
• 1X, 2X and Not 1X amplitudes with constant-Q filters for machine speeds of 60 to 2130 cpm.
• Three I/O options: internal terminations, external terminations, or internal barriers with internal terminations.
• Front-panel buffered outputs, short-circuit protected, for portable analysers.
• Immediate Danger alarm on loss of both transducers in hyper-compressor configuration.

Industrial Applications

Rider band and packing wear are among the main maintenance drivers on lubricated and non-lubricated reciprocating compressors, and unexpected rod contact can score the rod and cylinder liner. With the Bently Nevada 3500/72M on each throw, maintenance planners in Oman can track rider band wear trends and schedule overhauls on condition rather than on hours. Typical machines include gas gathering and gas lift compressors in the interior oil fields, compressors in refinery hydrogen service, and petrochemical units in Sohar and Duqm.

The Bently Nevada 3500/72M works alongside other rack modules such as the Bently Nevada 3500/45 Position I/O Module for axial and differential expansion on turbo trains, relay outputs from the 3500/32M 4-Channel Relay Module, and data transfer through the 3500/22M Transient Data Interface. Seven Star LLC helps compressor teams in Oman and the GCC select the right I/O option, confirm probe scale factors and plan spares for the Bently Nevada 3500/72M.

Related reciprocating compressor module: Bently Nevada 3500/70M Recip Impulse Velocity Monitor.

Ordering Information

The order code structure for the Bently Nevada 3500/72M is 3500/72M-AA-BB:

Related part numbers for the Bently Nevada 3500/72M, from the datasheet spares and accessories lists:

Technical Specifications

Key Bently Nevada 3500/72M data from datasheet 146478 Rev. M:

How to Order

For pricing on the Bently Nevada 3500/72M, email Seven Star LLC the complete 3500/72M-AA-BB code, or simply list the number of compressor throws, the probe scale factor, the termination style and the approval class. Our Muscat office replies with availability and delivery time for the monitor, its I/O module and any termination hardware; the full datasheet is in the documents tab above. Seven Star LLC supplies the Bently Nevada 3500/72M across Oman and the wider GCC.