Bently Nevada 330851-01-000-020-90-00-00 3300 XL 25 mm Probe

330851-01-000-020-90-00-00 3300 XL 25 mm Proximity Probe Explained

The Bently Nevada 330851-01-000-020-90-00-00 is a 3300 XL 25 mm proximity probe from the 330851 series. This is the large-tip probe in the 3300 XL family and it is built for measuring differential expansion on steam turbine generators, using a linear range of 12.7 mm (500 mils) at a nominal 0.787 V/mm (20 mV/mil) output. Seven Star LLC supplies the 330851-01-000-020-90-00-00 in Oman and the GCC as an independent supplier based in Muscat.

This particular part is a 1¼-12 threaded case, 2.0 in overall case length, with a 9.0 m (29.5 ft) probe lead and no armor (option 00). The 1¼-12 threaded case is the direct physical replacement for older English-thread 25 mm differential expansion probes. A 2.0 in case is the shorter of the standard English lengths, so it is used where the thread bore is shallow.

Decoding part number 330851-01-000-020-90-00-00

The datasheet builds a 330851 probe part number as 330851-AA-BBB-CCC-DD-EE-FF. Reading the ordering table for this part gives:

• AA = 01: probe case type, 1¼-12 threaded case
• BBB = 000: unthreaded length option, 0.0 in, which means the case is threaded over its whole length
• CCC = 020: overall case length, 2.0 in
• DD = 90: total probe lead length, 9.0 m (29.5 ft)
• EE = 00: no armor (option 00)
• FF = 00: no agency approvals ordered (option 00)

At 9.0 m it is a complete-length probe for the 9 m Proximitor Sensor and does not take an extension cable.

Technical specifications

Values above are for the probe within a complete 3300 XL 25 mm system (probe, extension cable and Proximitor Sensor) at 0 to +45 °C, gapped at 7.0 mm (275 mils) against a 4140 steel target, as stated in the datasheet.

How the 330851-01-000-020-90-00-00 measures gap

A 3300 XL Proximitor Sensor drives the probe tip coil with a radio-frequency signal. A conductive target within the field, such as a turbine collar or ramp, absorbs energy and changes the coil loading in proportion to the gap. The Proximitor demodulates that change into a negative dc voltage, which the monitor reads as displacement. The 25 mm tip gives a wide field and therefore a wide linear window, which is the reason this system is chosen when a rotor moves axially by several millimetres and a standard 8 mm probe would run out of range.

Differential expansion measurements use two transducers: either both observing the same side of a collar, which gives redundancy, or two complementary inputs observing opposite sides of a collar, which doubles the measurable range, or one probe on a ramp with a second compensating for radial movement. The same-side arrangement is the preferred one when enough collar height exists.

Where the 330851-01-000-020-90-00-00 fits in the system

A complete 25 mm channel consists of the probe, an optional extension cable (the 330854 series in 4.0 m or 8.0 m lengths) and a 3300 XL 25 mm Proximitor Sensor from the 330850 series, which is offered for panel or DIN mounting in 5 m or 9 m system lengths. The probe length plus extension cable must equal the Proximitor Sensor total length. It is typical for retrofits where the existing machine already has a 1¼-12 tapped boss and the plant wants a drop-in replacement with FluidLoc cable that keeps lube oil out of the cable interior.

The 3300 XL 25 mm probe is described as a replacement for the 7200 25 mm, 7200 35 mm and 25 mm DE integral systems, and the Proximitor output matches those systems so monitor configuration does not need to change. When upgrading, every component of the channel (probe, extension cable and Proximitor Sensor) has to be replaced with 3300 XL 25 mm parts. Related probes in the same 330851 family include 330851-01-000-020-90-00-00, 330851-03-000-020-90-00-00, 330851-04-000-020-90-00-00, 330851-04-000-020-10-00-00, 330851-04-000-020-50-01-00 and 330851-05-000-060-10-00-00.

Selection and ordering checklist for 330851-01-000-020-90-00-00

• Confirm the case type against the existing bore or holder: thread size and pitch, or smooth diameter and exit direction.
• Confirm the overall case length and the unthreaded length from the old probe drawing or the installation drawing.
• Match the lead length to the Proximitor Sensor: a 5 m probe works only with the 5 m sensor; shorter leads add the right extension cable to reach the system length.
• Decide whether armor is required for lead routing, and note the 28 mm minimum probe length with armor.
• State whether approvals are needed for the installation area, since this part number carries FF = 00.
• Check the target material: Proximitor Sensors are calibrated at the factory to AISI 4140 steel unless another material is requested.

Installation, commissioning and maintenance of 330851-01-000-020-90-00-00

Install the probe so that the tip sits in the middle of the linear range, which for this system corresponds to a 7.0 mm (275 mil) gap. Set the gap with the system powered and measure the dc voltage at the Proximitor output. When the sliding bracket is used, move the probe through its range and compare the voltage trace with the dial indicator reading to verify the installation, then repeat the check periodically.

Connectors are finger tight only. Fit the connector protectors supplied with the probe and extension cable, keep them clean, and never exceed the 25.4 mm minimum bend radius. Because the probe is designed to seal a differential pressure with a Viton O-ring and compression seal but is not pressure tested before shipment, the user remains responsible for containing process fluid if the seal were to leak. Exposure of the probe to low temperatures can damage the seal, so store and handle according to the datasheet range.

For maintenance, keep a spare probe of the same dimensions where the machine has long overhaul intervals. A probe with a bent cable, a damaged tip or a changed resistance reading should be replaced as a set with its matched extension cable and Proximitor Sensor rather than mixing generations.

Typical applications in Oman and the GCC

Large steam turbine generators in power and desalination plants across Oman and the GCC are the main users of this probe. Hot ambient conditions, high humidity and airborne dust are normal at these sites, and the FluidLoc cable, PEEK tip and 200 °C probe rating suit the elevated casing temperatures found near the turbine thrust bearing. Differential expansion monitoring protects the tight axial clearances during start-up, load changes and shutdown, which is when a rotor and casing grow at different rates. Industrial steam turbines in petrochemical and refining plants use the same measurement.

Variants in the 330851 family

Information to send with your 330851-01-000-020-90-00-00 RFQ

• Full part number and quantity.
• Machine tag, turbine make and model, and whether this is a replacement or new installation.
• Existing probe case type, thread or diameter, and case length.
• Proximitor Sensor part number in service (330850 series, 5 m or 9 m, panel or DIN mount) and extension cable length if any.
• Required approvals, armor and delivery location.

Related Bently Nevada products: Bently Nevada 330105-02-12-10-02-05 3300 XL Probe, Bently Nevada 3300 XL 25 mm Proximitor Sensor 330850-51-CN, Bently Nevada 32000-00-00-04-470-01-02 Proximity Probe Housing, Bently Nevada 3300 XL 8mm Probe 330103-00-05-10-01-00, Bently Nevada 3300 XL 8mm Proximity Transducer System and Bently Nevada 990-05-70-02-00 2-Wire Vibration Transmitter.

Documents and quotation

The official Bently Nevada 3300 XL datasheet (document 163236) covering the 330851-01-000-020-90-00-00 ordering options is attached on this page. Read the ordering table together with the machine drawings before confirming the part number.

Send the part number 330851-01-000-020-90-00-00 and your quantity through the RFQ form and our team in Muscat will confirm availability and lead time.