Bently Nevada 3500/42M Proximitor Seismic Monitor

TL;DR: The Bently Nevada 3500/42M is a four-channel monitor that accepts input from both proximity and seismic transducers – “Accepts from 1 to 4 proximity, velocity or acceleration transducer signals”, in the datasheet’s words. Channels are programmed in pairs, so channels 1-2 can run one function while 3-4 run the same or a different one. Against the 3500/40M it adds Acceleration, Velocity, Acceleration II, Velocity II, Shaft Absolute and Circular Acceptance Region channel types, plus a +4 to +20 mA record output for each channel. It takes one full-height front slot and one full-height rear I/O slot, draws 7.7 W typical, and the current monitor spare part number is 176449-02. TenBN stocks /42M monitors and I/O modules with live availability listed below.

What is the 3500/42M?

It is the mixed-signal vibration channel in a 3500 rack. Where the 3500/40M is restricted to Bently Nevada proximity transducers, the /42M will accept a 3300 XL eddy-current system, a Velomitor, a Seismoprobe or an HTVS accelerometer on the same four channels, and it can mix them within one module depending on the I/O module fitted. The programmable channel functions listed in datasheet 143694 are radial vibration, REBAM, thrust position, acceleration, differential expansion, shaft absolute, eccentricity, circular acceptance region and velocity.

Channel pairing is the detail most people miss when they quote a /42M against four discrete single-channel inputs. Each pair shares its configuration, so you get two independent function types per module, not four – for example a bearing pair configured as radial vibration X/Y, and a casing pair configured as velocity. If your design genuinely needs four different channel types in one slot, that is two /42M modules, and the 14-slot rack has room for it: Baker Hughes quotes 4-channel monitors reaching 56 monitoring channels in a full-size rack.

The record outputs are the other half of the story. The /42M provides “individual recorder values for each channel” – four +4 to +20 mA outputs – and 162096 states plainly that “The 3500/40M does NOT provide 4 to 20 mA outputs”. If a DCS has to trend the waveform-derived values, that alone decides between the two modules.

3500/42M specifications

From Baker Hughes datasheet 143694 Rev. AE (3500/42M Proximitor Seismic Monitor), with system-level figures from 162096.

Two things this table deliberately does not claim. Datasheet 143694 gives no rack supply-voltage or bus-current rating for the /42M – power is a 3500/15 module property, covered on our power supply page – and it makes no SIL statement for this module. The 3500 system datasheet mentions SIL 1 and SIL 2 “for various 3500 monitors” without naming the /42M, so we will not either.

Compatible racks and slots

The /42M sits in any standard 3500/05 rack: the full-size 19-inch rack with 14 general module slots, or the 7-slot mini rack. It is a full-height module – “half-height” appears nowhere in 143694, and the only half-height monitor in the 3500 range is the 3500/25 Keyphasor. The reserved left-hand end of the rack belongs to the two power supplies and the transient data interface; every other position is available.

The rear slot must be an I/O module matched to the transducer mix. That is the part of a 3500/42M order people get wrong most often: the front module is the same part every time, and it is the rear I/O module that decides which sensors you can actually connect. The I/O module installs at the rear of the rack for panel-mount systems and above the main module for bulkhead-mount systems, and it is not hot-swappable.

If you are replacing a /40M with a /42M to gain record outputs or seismic channels, the front modules are not interchangeable in the sense that the rear I/O has to be re-evaluated too – the /42M’s barrier I/O parts differ from the /40M’s, and the terminal blocks are separate order lines.

Installation and wiring

Field wiring terminates on the I/O module, never on the monitor itself. With internal termination I/O the transducer wiring lands straight on the rear module’s terminals – the proximitor and seismic module shows four terminals per channel (PWR/B, COM, SIG/A, SHLD). With external termination I/O the field runs land at ET blocks beside the rack and return on a single prefabricated multi-pin cable. Both proximitor and shaft-absolute ET blocks exist in Euro-connector and terminal-strip styles, and the cable is ordered separately: 129525-AAAA-BB from the transducer to the ET block, or 129529-AAAA-BB for the ET block lead, in 5, 7, 10, 25, 50 or 100 ft (1.5 to 30.5 m), assembled or unassembled.

External termination blocks cannot be used with internal-termination I/O modules, and 143694 warns that blocks and cable must be ordered separately for each I/O module. Decide the termination scheme at order time – it is fixed by the I/O part number, not by configuration.

Hazardous-area work is drawing-driven. Non-barrier I/O follows drawing 149243 or 149244; internal-barrier I/O follows drawing 138547. The barrier I/O variants (135489-01, -02 and -03) are supplied as 4 x proximitor/acceleration, 2 + 2 proximitor and Velomitor, or 4 x Velomitor, they remove the external-termination option because intrinsically safe wiring cannot share a multi-core cable, they narrow the operating window to 0 to +65 °C, and they add 74 mm (3 in) to rack depth. Published barrier parameters for the /42M proximitor circuit are Vmax 26.80 V (PWR) and 14.05 V (SIG), Imax 112.8 mA (PWR) and 2.82 mA (SIG); the seismic circuit is Vmax 27.25 V, Imax 91.8 mA. Do not reuse /40M barrier figures on a /42M – they are different.

Configuration is done in 3500 System Configuration Software and the resulting rack file lives in the interface module. The firmware floors in 143694 are 3500/01 v2.50, 3500/02 v2.20 and 3500/03 v1.21 for a base /42M; shaft absolute needs /42M firmware revision B with 3500/01 v2.61 and DM2000 v3.10, and Acceleration II, Velocity II and circular acceptance region need /42M firmware 2.10 with 3500/01 v3.20 and DM2000 v3.30.

Indicators and diagnosis

The front panel carries three LEDs: OK for correct operation, TX/RX for communication with the rest of the rack, and BYPASS for Bypass mode. There is no published per-channel LED and, importantly, no published /42M error-code table – 143694 contains none, so any “3500/42M fault code list” you find online is a dealer invention.

What the range does give you is suppression instead of codes. The 3500 system “incorporates numerous self-monitoring functions that can identify faults in the monitor modules and their connected transducers, annunciate and identify problems via appropriate error codes, and suppress channel operation automatically when a failure could compromise correct operation of the system”, and OK detection routines “continuously check the integrity of each transducer and associated field wiring”. A channel that reads Not OK or absent is normally a suppressed channel, so the honest order of diagnosis is: check Bypass state first, then whether the rear I/O module matches what the monitor expects (a replaced I/O module that has not been reconciled by firmware update reports an I/O module mismatch), then the transducer and its leads, then the monitor.

Two /42M-specific checks are worth knowing before you condemn hardware. Acceleration and velocity channels configured as Acceleration or Velocity “provide only direct amplitude” – if your display is missing 1X and 2X on such a channel, that is the configured channel type, not a fault; select Acceleration II or Velocity II to get 1X and 2X amplitude and phase plus bias voltage. And on REBAM, one channel of a pair can be enabled in certain configurations, with the achievable limit depending on maximum machine speed against the number of rolling elements – a single-channel REBAM arrangement is a legitimate configuration, not a broken second channel.

A Danger that has latched is reset from the rack: a TDI front-panel reset clears latched alarms and latched Not OK conditions, and the rack event log retains 2000 alarm events and 1000 system events, so the trip sequence can be reconstructed rather than argued about.

Ordering codes

The datasheet prints the order string as 3500/42 - AA - BB. Note there is no “M” in the printed string – “3500/42M-01-00” style codes are dealer usage, which matters when you are trying to match a nameplate to an official price or spares list.

There is no AA = 03 option for the /42M, and BB accepts only 00, 01 and 02 – a code quoted to you as 3500/42-09-05 is not a valid combination against 143694, and we will confirm what the physical label actually says before supplying it. Documented monitor spare is 176449-02; the user guide is 143489. Part numbers such as 140734-01 and 140734-02 circulate widely on reseller listings but do not appear anywhere in 143694, 141535 or 162096 – if you are being quoted one, ask which datasheet revision lists it.

3500/42M parts we can supply

Part number

Frequently asked questions

What is the difference between the 3500/40M and the 3500/42M?

Input type and recording. Both are four-channel, both take one front slot and one rear I/O slot, and both use Alert on every measured value with Danger on any two. The 3500/40M accepts Bently Nevada proximity transducers only and provides no analogue record outputs. The 3500/42M accepts proximity, velocity or acceleration transducers, adds acceleration, velocity, acceleration II, velocity II, shaft absolute and circular acceptance region channel types, and provides an individual +4 to +20 mA record output for each channel. The /42M also offers a wider I/O module range – options 01, 02 and 04 through 10 against the /40M’s 01 to 03.

How many channels does a 3500/42M have?

Four, accepting from 1 to 4 proximity, velocity or acceleration transducer signals. They are programmed in pairs, however, so channels 1-2 perform one function while channels 3-4 perform another or the same one. Plan on two independent function types per module.

Can the 3500/42M take an accelerometer and a proximitor in the same rack?

Yes, and in the same module if the I/O variant supports the mix – option 05 pairs two proximitor/acceleration channels with two Velomitor channels, and option 09 or 10 covers proximitor, Velomitor or HTVS. The transducer family is a property of the rear I/O module, so the part number you order has to match the sensor population you intend to connect.

Does the 3500/42M have 4-20 mA outputs?

Yes – four, one per channel, +4 to +20 mA proportional to monitor full scale, driving 0-600 Ω, with 0.3662 µA per-bit resolution and roughly ±0.25% error at room temperature. Monitor operation is unaffected by short circuits on the recorder outputs. The 3500/40M does not provide them. Treat both as annunciation and trending paths: Baker Hughes is explicit that record outputs and Modbus do not carry the fault tolerance required for machinery protection or shutdown, so the trip path must end in relay module contacts.

Which slot does the 3500/42M occupy?

One full-height front slot for the monitor and one full-height rear slot for its I/O module, in any general-purpose position. Only the left-hand end is reserved – that is where the two power supplies and the transient data interface go, and each rack requires one TDI immediately adjacent to the power supply slot. A standard 14-slot rack reaches 56 monitoring channels when built from four-channel monitors; a mini rack has 7 monitor slots.

What do the LEDs on a 3500/42M mean, and is there a fault code list?

Three LEDs: OK, TX/RX and BYPASS. There is no published fault-code table for the /42M – datasheet 143694 contains none – and the system responds to detected faults by suppressing the affected channels rather than reporting a plausible wrong value. So a dead or Not OK channel usually means suppression: check bypass state, then I/O module match and firmware, then the transducer and field wiring.

Is 140734-01 a genuine 3500/42M part number?

Not one we can source. 140734-01 and 140734-02 appear on reseller listings but not in datasheet 143694, 141535 or 162096. The monitor spare the official documentation does list is 176449-02. We stock both kinds of stock number because the market uses both, but when you order we verify against the label on your module rather than the number in an advertisement.

Can I swap a 3500/42M I/O module while the rack is powered?

No. The monitors are hot-insertable, but I/O modules are explicitly not hot-swappable, so replacing rear I/O is a de-energised job. Also budget a firmware reconciliation step: an I/O module that does not match the monitor’s expected level is reported as an I/O module mismatch and its channels are suppressed until the firmware is aligned.

Request a 3500/42M quote

Send the full code from the front label – for example 3500/42-01-00 – and, if you are only changing the rear module, the I/O part number printed on it (128229-01, 135489-02, 138708-01, 140471-01 and the rest are all documented). We will confirm the transducer mix, the termination scheme, the approval code your area classification needs and current stock. Prices are quoted per enquiry and are not published on this site.

See also the 3500 system complete guide for how channel monitors, relay modules and record outputs fit together in a compliant protection train, the 32000 housings page for metric proximitor housings, and the 3500/60 for the temperature channels in the same rack.