Bentley 3300/50 Speed Monitoring Module (Tachometer Monitor) Detailed Product Description

I. Product Overview

The Bentley 3300/50 is a single-channel speed monitoring module within the 3300 series TSI (Turbo Generator Instrumentation) system of Baker Hughes (formerly part of General Electric - Bentley Nevada). It is primarily used for continuous online precise monitoring of the shaft speed, rotor acceleration/deceleration, and zero-speed in rotating machinery.

This module adopts a 19-inch standard rack design, supports hot swapping, and can be installed in the same rack with vibration, shaft displacement, eccentricity, temperature, etc. modules, sharing the backplane - 24V DC power supply and system bus. It is compatible with Bentley eddy current probes and magnetic speed sensors, and has built-in dual-channel sensor redundancy input + hardware voting logic. In case of a broken wire, short circuit, or abnormal signal on one sensor, the module automatically switches to the normal channel and lights up the corresponding fault LED to prevent false alarms or monitoring interruption, significantly enhancing reliability.

It is widely used in steam turbines, gas turbines, centrifugal compressors, large fans, pumps, motors, and other key rotating equipment in industries such as power, petrochemicals, metallurgy, oil and gas, water treatment, etc., for overspeed/underspeed warning, abnormal monitoring during start-up/shutdown speed increase/decrease, and zero-speed interlock protection; it cannot be used independently as a main overspeed protection device, but is only for status monitoring and warning purposes.

II. Model Coding Rules (3300/50-XX-XX-XX-XX)

3300: Bentley 3300 modular TSI system, unified rack, centralized power supply, hot swapping, multi-module mixed installation architecture.

50: Function code, speed monitoring module (Tachometer), responsible for speed, acceleration/deceleration, and zero-speed monitoring.

The 1st position (monitoring type): 01 = standard speed monitoring; 02 = speed + acceleration enhancement monitoring; 03 = zero-speed dedicated monitoring.

The 2nd position (relay configuration): 01 = single relay (only alert ALERT); 02 = dual relays (alert ALERT + danger DANGER).

The 3rd position (certification level): 00 = no certification; 01 = general industrial safety certification; 02 = explosion-proof intrinsic safety certification (Ex ia).

The 4th position (safety barrier configuration): 00 = no safety barrier; 01 = isolated safety barrier; 02 = intrinsic safety safety barrier (applicable in explosion-proof zone).

III. Core Functions

1. Dual sensor redundancy input and hardware voting

Single-channel design, supports connection of two independent speed sensors (eddy current probe or magnetic sensor), built-in hardware voting circuit. When any one of the sensors has a broken wire, short circuit, signal out of tolerance, or no signal, the module automatically switches to the normal channel and lights up the corresponding fault LED to prevent false alarms or machine shutdown caused by a single sensor failure, significantly enhancing reliability.

2. High-precision speed, acceleration, and zero-speed monitoring

Speed measurement: range 1–99999 RPM programmable, accuracy ≤ ±1 RPM (25°C), resolution 0.1 RPM.

Acceleration / deceleration: range **-9999~+9999 RPM/min**, response time < 100 ms, captures speed sudden changes, ascension or descent anomalies.

Zero-speed detection: threshold 0–100 RPM programmable, used for unit shutdown confirmation, disk rotation interlock, preventing false start or reverse rotation.

Each revolution pulse count: 1–60 pulses/revolution programmable, suitable for different speed measurement gears or keyways.

3. Graded relay alarm output According to the model configuration, one or two SPDT relays are provided, epoxy resin sealed, moisture-proof, dust-proof and anti-interference.

Single relay: ALERT (warning), used for alerting when the rotational speed deviates from the normal range.

Double relays: ALERT (warning) + DANGER (danger), used to trigger interlock when there is severe overspeed / underspeed.

Contact specifications: 250V AC/5A, 30V DC/5A. Can directly drive sound and light alarms, DCS/PLC or interlock circuits.

Alarm threshold and delay: The alarm threshold for rotational speed and acceleration is independently set. The delay can be adjusted from 0 to 10 seconds. Instantaneous fluctuations are filtered.

4. Front panel display and local configuration

Display: Analog header + digital window, real-time display of rotational speed value; OK, ALERT, DANGER, BYPASS four groups of LEDs, intuitively display running, alarm, bypass status.

Configuration: Key-based local programming, parameters such as range, alarm threshold, zero rotational speed value, pulse per revolution, alarm delay can be set without an upper computer.

5. Isolated buffer signal output

The rear terminals provide two isolated analog outputs (4–20mA or 0–10V selectable), electrically isolated from the power supply, input signal, and can send rotational speed / acceleration signals to recorders, oscilloscopes or external systems for data recording, trend analysis and fault tracing.

6. Comprehensive self-diagnosis and fault identification

24-hour real-time monitoring: sensor open circuit / short circuit, signal over-limit, power supply abnormality, module hardware failure. Can distinguish real rotational speed abnormality from sensor / circuit failure. The panel LED clearly indicates the fault type, facilitating rapid troubleshooting.

7. Strong anti-interference and system integration

Metal shielding shell, input/output/power isolation ≥ 2500V AC, anti-common-mode interference, suitable for variable frequency drives, high-voltage cabinets and other strong electromagnetic environments.

Compatible with 3300 series system bus, can be connected to System 1 status monitoring software to achieve remote configuration, data storage, trend analysis, fault recording and remote access.

Four. Technical parameters

Measurement parameters

Monitoring channels: single channel (dual sensor redundant input).

Compatible sensors: Bently eddy current speed probe, magnetic-electric speed sensor (magnetic-electric not recommended for zero rotational speed).

Rotational speed range: 1–99999 RPM (programmable).

Acceleration range: -9999 to +9999 RPM/min.

Zero rotational speed threshold: 0–100 RPM (programmable).

Measurement accuracy: rotational speed ≤ ±1 RPM (25℃); acceleration ≤ ±20 RPM/min.

Frequency response: 1 Hz–10 kHz (automatic threshold).

Input impedance: 10 kΩ.

Electrical parameters

Working power supply: -24V DC (±10%), backplane power supply.

Power consumption: typical 2.5 W, maximum ≤ 3 W.

Sensor input: two pulse signals, peak ±10 V.

Relay output: 1–2 SPDT, 250V AC/5A, 30V DC/5A.

Buffer output: two isolated analog signals (4–20mA/0–10V selectable).

Isolation strength: input/output/power isolation ≥ 2500V AC; explosion-proof models have built-in intrinsically safe safety barrier (Ex ia IIC T4 Ga).

Environmental and mechanical parameters

Operating temperature: standard type - 30℃ to +65℃; explosion-proof type - 20℃ to +60℃.

Storage temperature: -40℃ to +85℃.

Relative humidity: 0%–95% (no condensation).

Installation method: 19-inch standard rack slot, hot-swappable. Dimensions: 203 mm (height) × 330 mm (depth) × 51 mm (width).

Weight: Approximately 1.5 kg.

Protection level: IP20 (for installation inside the control cabinet).

Certification and Compliance

Industry standards: Compliant with API 670 Rotating Machinery Monitoring Protection Standard.

Electromagnetic compatibility: CE certification, compliant with EN 61000-6-2/4.

Safety and environmental protection: UL certification, RoHS compliance.

Explosion-proof certification: Some models are Ex ia IIC T4 Ga, suitable for flammable and explosive hazardous areas.

VII. Structural Design

The module is an integrated compact frame structure, divided into the front panel, internal circuitry, and rear terminal block. The front panel integrates display, LED, and operation buttons, facilitating on-site observation and configuration. The internal circuitry includes dual-channel signal conditioning, hardware voting, speed/acceleration calculation, alarm comparison, relay drive, and (for explosion-proof models) intrinsically safe safety barrier unit. The function zones are clearly defined, the layout is compact, the shielding is good, and the internal interference is suppressed. The rear terminal block is clearly zoned and clearly labeled, covering sensor input, relay output, buffer output, power and communication interfaces; for explosion-proof models, the terminals in the hazardous area and the safe area are physically isolated, in line with intrinsically safe wiring specifications. The module and the frame use gold-plated connectors, with reliable contact, wear-resistant, anti-oxidation, stable electrical connection during hot plugging, and no need to shut down the module for replacement.

VIII. System Compatibility

Hardware Compatibility

Frame and power supply: Compatible with 3300 series 19-inch frames, power modules, system monitoring modules, and can be installed with vibration, shaft displacement, temperature, etc. modules.

Sensors: Fully compatible with original Bently electromagnetic flow rate probes and magneto-electric speed sensors; for explosion-proof models, compatible with intrinsically safe sensors.

Output Connection: Relay contacts connected to audible and visual alarms, DCS/PLC, interlock circuits; buffer output connected to recorders, oscilloscopes, and external instruments.

Software Compatibility

Configuration software: Compatible with 3300 series dedicated configuration software, supporting remote parameter configuration, alarm logic editing, firmware upgrade.

Monitoring software: Connected to System 1 platform, achieving real-time data, trend analysis, fault recording, report generation, and remote access.

IX. Typical Application Scenarios

Power Industry: Turbines for thermal power / gas turbines, generators, induced draft fans, supply fans, speed monitoring for these components; abnormal speed rise/fall during start-up/shutdown warning; dual-level alarm to ensure safe start-up/shutdown and stable operation of the unit.

Petrochemical Industry: Centrifugal compressors in explosion-proof/non-explosion-proof areas, process turbines, large-scale process pumps speed monitoring; overspeed/underspeed classification warning; speed mutation, acceleration abnormality identification, preventing production interruption.

Metallurgical Industry: High-temperature fan, sintering fan, large-scale transmission motor speed monitoring; abnormal start-up/shutdown warning; dual-level alarm linkage interlock to reduce fault shutdown risk.

General Industry: Cement, papermaking, water treatment, etc. industries for grinding mills, fans, water pumps, etc., online speed monitoring, zero-speed interlock, classification warning, extending equipment lifespan, reducing operation and maintenance costs.

IX. Installation and Maintenance Specifications Installation Requirements

Rack Installation: Push the 3300 rack slot smoothly and ensure that the rear connectors are fully engaged. Tighten the panel screws.

Sensor Wiring: Connect the two sensor cables according to the channel markings, with the shielding layer grounded at one end; for explosion-proof areas, follow the safety instrumented system specifications for construction.

Alarm Wiring: Distinguish between ALERT and DANGER contacts, connect them to the alarm/interlock circuit, and confirm the logic is correct.

Power-On Configuration: Confirm that the -24V DC power supply is normal. Set the range, alarm threshold, zero speed value, pulse per revolution, delay, and save through the panel or software.

Sensor Installation: Fix the probe at the shaft end or the speed measuring gear, strictly control the installation gap, secure it firmly, and ensure the cable protection is in place.

Daily Maintenance

Inspection: Observe the panel display and LED status to confirm normal speed and no fault alarms; check the terminals for no looseness, oxidation, or overheating; ensure the wiring seal in the explosion-proof area is intact.

Calibration: Use a standard speed generator to calibrate the accuracy annually, in accordance with API 670; conduct regular inspections of the safety barrier insulation performance of the explosion-proof models.

Cleaning: Regularly clean the modules and rack of accumulated dust to ensure ventilation and heat dissipation, and avoid short circuits or poor heat dissipation.

Replacement of Spare Parts: When the module, sensor, or cable is damaged, it must use the original Bentley same-model spare parts; the explosion-proof area spare parts must have explosion-proof certification.

IX. Usage Precautions

The ordinary model is non-explosion-proof and must not be used in flammable and explosive hazardous areas; the explosion-proof model must strictly follow the explosion-proof installation specifications.

It cannot be used independently as the main overspeed protection device; it is only used for condition monitoring and early warning; the key unit's overspeed protection requires a dedicated triple-redundant overspeed protection system.

It must be paired with the original Bentley speed sensor; different specifications cannot be mixed; for the explosion-proof area, use the intrinsically safe sensor; otherwise, the signal will not match or the measurement will fail.

The installation gap of the sensor must be strictly set according to the manual; abnormal gaps will cause signal distortion and increased error.

It is prohibited to disassemble the module, modify the internal circuitry, or modify the sensor calibration parameters privately; violation will result in equipment damage, invalid warranty; it is strictly prohibited to remove the safety barrier circuit.

Before wiring, maintenance, or replacing the module, cut off the power supply of the rack; operations in the explosion-proof area comply with explosion-proof safety regulations to prevent short circuits, electric shock, or explosions.

Alarm threshold and delay must be combined with the unit's process settings; improper parameters will lead to frequent false alarms or warning failures.

The installation location should be far from power frequency converters, transformers, high-voltage cabinets, etc., which are strong electromagnetic interference sources, to reduce signal interference and ensure stable monitoring.