Bently Nevada Hardware: More Than Meets The Eye

Did you know that your Bently Nevada monitor may be more powerful than you think? Hidden in that state-of-the-art machinery protection device is more than simply the ability to trend overall vibration amplitudes. Chances are you have more machinery condition information than you thought!

When considering Bently Nevada hardware and software, they can be broken down into 3 basic tiers. First would be machinery protection – where sensors are connected to the monitor, alert & danger setpoints are configured, and relay contacts are enabled based on the desired logic. Second would be basic condition monitoring – where that protection is combined with enhanced capability for trending several variables. And finally, advanced condition monitoring – where all of those in-monitor variables AND the rich waveform data are transmitted to System 1 for analysis & diagnostics. This article will discuss the second tier.

Most users with a 3500 rack utilize it for more than the basic protection capabilities. While the 3500 was built with the utmost reliability for protection in mind, it was ALSO designed to offer far more value. The first level of trending would be via the recorder output contacts. Most vibration cards (3500/4x) and some other cards (3500/50M, 61, 64, 70M, 72M) include these outputs as an option on the IO module. Likewise, the 2300 and 1900/65A Bently Nevada monitors also offer recorder outputs.

While the ability to monitor the 4-20mA output from a monitor is useful for control and trending, it is limited in that it is only ONE variable per channel – typically Overall/Direct Amplitude. Granted, it’s better than nothing – but there’s more to the story.

What Else Is There?


At a very basic level, every vibration sensor will have either gap voltage (proximity probes) or bias voltage (seismic sensors) measured in the card.

Gap voltage is useful in several ways:

  • It gives an indication of the sensor health. Generally speaking, a proximity probe will be gapped to -10V upon installation. If the voltage reading is close to 0V or -24V, that is likely an indication that something is wrong with the sensor system itself (probe, cable or Proximitor).

  • It gives additional insight to the machine condition. The AC component of the proximity probe sensor gives the vibration reading – how much the target surface is moving back & forth. The DC component (or Gap Voltage) gives an average reading of how far away the target surface is from the sensor tip. If the vibration changes in a significant way during normal operation, a correlating shift in Gap Voltage can provide some value regarding whether the shaft shifted one way or another within the bearing.

1X Amplitude & Phase

If a Keyphasor is present in the rack, and the vibration sensors are properly associated, the card will analyze the vibration and provide a filtered 1X Amplitude & Phase measurement. In real time, you can see how much of the overall vibration is occurring at the same frequency as the rotation of the shaft! Why is this important? Imbalance usually manifests as an increase in 1X amplitude. Shaft Bow will show as a clear 1X component at lower speeds. Even rubs can occasionally show up as 1X vibration.

However, it can be almost as informative to see NO change in 1X vibration. If the overall amplitude changes, but the 1X stays constant, this is an indication that some other frequency component is present and affecting the vibration. How do you know which frequency component? Well, that’s where System 1 comes in handy…

Also useful is the 1X Phase measurement. Typically, during steady state operation with no change in process parameters, the phase should remain constant during operation. If phase starts to change, that is an indication that the nature of the vibration is changing – even if the amplitude doesn’t. Thermal effects, slight rubs, etc can affect the phase behavior of a vibration signature. And, of course, phase is critical for balancing calculations.

2X Amplitude & Phase

As above, the monitor will also calculate the component of vibration that occurs at twice the running speed … or 2X vibration. This can be very useful for identifying malfunctions such as misalignment shaft cracks, and others.

Other useful variables

Not 1X

As the name implies, this variable trends everything except the 1X amplitude – which can be useful if you’d like to alarm off of something other than the 1X.  This can be an indicator of fluid instabilities in fluid film bearings or other problems like compressor surge and stall.

Smax Amplitude

When two proximity probes are mounted orthogonally (X&Y) and associated to each other, they can measure the orbit of the shaft movement. The situation may occur where the maximum amount of vibration does not occur in the same plane as either of those sensors. The Smax measurement looks at the orbit shape and calculates the maximum displacement from that. As such, this measurement is not available if only one sensor is installed.

Crosshead Acceleration Bands

When an accelerometer is mounted on the crosshead of a reciprocating compressor, the overall vibration is only a very small part of the story. The real value comes in identifying at which point in the stroke of that piston the vibration occurs. In a 3500/70 monitor, the Impulse Accel measurement provides for 6 spectral bands that can be configured as a function of X° crank angle rotation. For example 10° on either side of Top Dead Center or Bottom Dead Center (0° or 180°) can show indications of liquid ingestion. Bands around other points can highlight indications of loose valves, improper lubrication and other symptoms.

All 6 of these bands (for every channel) are available for trending, direct from the monitor. If you’d like to see the nature of the vibration signature or add additional bands, System 1 software provides deeper analysis capabilities.

Rod Position

When 1 or 2 sensors are mounted on a reciprocating compressor packing case to measure the movement of the piston rod, they can be configured to measure the Rod Position amplitude (how far the piston is from the centerline of the cylinder). However, they will also be measuring the Rod Position Angle (where is the piston moving – top left, straight down, etc?) and Crank Angle (at which point in the stroke is the maximum deviation?). 

In addition to the above measurements, the Rod Position channel also offers the Pk-Pk Displacement of the rod movement as a variable. This helps to identify if the piston rod is moving or flexing more than before (can occur during various compressor malfunctions).

Cylinder Pressure

When cylinder pressure sensors are mounted on a reciprocating compressor cylinder, a wealth of health-related information is opened up:

  • Discharge & Suction Pressures

  • Maximum & Minimum Pressures

  • Compression Ratio

  • Peak Rod Compression/Tension

  • Degrees of Rod Reversal – recommended by API618 for crosshead pin health

Alarm Setpoints

At first glance, alarm setpoints doesn’t seem like an obvious “variable” that might be of interest. However, it can be very useful to know what the setpoints are for a particular point when evaluating how close a machine is to a danger condition.

So, That’s It?

Not quite – the above items have only referenced the 3500 monitoring system. What about other Bently Nevada hardware?


The ADAPT family of monitor provides incredibly powerful processing in a very compact package. Able to monitor up to 12 vibration channels (plus 2 speed/ Keyphasor), each channel is able to not only measure the above-mentioned Direct, 1X, 2X and voltages – but also:

  • Configurable nX vectors: want to track blade pass frequency? Gear mesh frequencies? Etc?

  • Vector measurements for multiple shafts on a single channel: for example, you could associate a single accelerometer on a gearbox to 2 different Keyphasors and track nX vectors … on one channel!

  • Multiple custom bandpass measurements for each channel: set high pass and low pass corner frequencies to measure the energy within a certain frequency range.

3701/4x ADAPT

Each vibration input channel in the 1900/65A has the ability to configure 3 vibration variables plus the bias or gap voltage. For example, with a single accelerometer connected, you could measure Overall Acceleration, Integrated Velocity and Enveloped Acceleration … at the same time! With a Velocity sensor connected, you could measure Velocity and Integrated Displacement … and a third variable (perhaps a bandpass frequency).


Similar to the 1900/65A, the 2300 Vibration monitor also has the ability to configure several variables for each vibration channel (Direct 0-pk, pk-pk, Direct rms, Derived pk, integrated direct pk,).

The 2300 monitor has the added benefit of direct connectivity to System 1. As with the 3500, this allows for the calculation of additional software variables and the analysis of Waveforms!

2300 Vibration Monitor

The Trendmaster system is distributed network of Dynamic Scanning Modules (DSMs) used for condition monitoring. While primarily intended as a cost effective way to bring data to System 1 for analysis, the System processes the data in the monitor and calculates a lot of the more common variables mentioned above (Direct, Gap, 1X Amplitude/Phase, etc), as well as some that are more suited for rolling element bearing condition monitoring (Enveloped Pk or RMS, High Frequency, Prime Spike, etc).

TrendMaster Pro

The TDISecure is a multi-channel data acquisition device that acquires up to 24 channels of dynamic signals and 24 channels of process measurement inputs. The variables available within the dynamic channels are identical to those in the 3500/42M monitor (Direct, Gap, 1X, 2X, Not 1X, Smax).

TDISecure Communications Processor

Woah, Cool – How Do I Get To This Data?

The good news is that accessing all this great data is quite simple – Modbus! While the recorder outputs (4-20mA) on most monitors provide a simple and secure method of trending data, they are limited to a single variable. Modbus allows you to trend EVERYTHING! Static variables, statuses, alarm setpoints, time and date information, etc – it’s all there, ready for the taking.


Other than the basic measurement of each card (ie. Direct & Gap), the additional variables are not checked by default. In the 3500 monitor configuration software, open the configuration for each channel and check the box(es) for the variables you’d like to measure.

Then, to actually export those measurements, you need to enable the Modbus registers in your 3500/92 card. If all you’re doing now is reading recorder outputs, you may want to consider adding a 3500/92 to your rack – the vastly improved machinery condition information should offset the minor additional cost very quickly!

Other Monitors

ADAPT 3701/4x – The 3701/4x monitors include two Ethernet ports per CPU which provide Ethernet TCP/IP communications capabilities. Standard industrial protocols (capability included at no extra charge!) are Modbus TCP/IP and Ethernet Global Data (EGD). Configuration is done through the standard BNMC software.

1900/65A – A Modbus Gateway option allows the monitor to provide static variables, statuses, event list, time and date information directly to any Modbus client. You can include this option when purchasing, or you can upgrade monitors without the Modbus Gateway by ordering the 1900/01 Communications Upgrade. It’s a simple firmware update (no additional hardware needed) and configuration is done through the standard 1900 Configuration Software.

2300 – All 2300 monitors come with Modbus capability included. No additional cost! Configuration is done through the standard BNMC software.

TrendMaster - All DSMs include Modbus over TCP/IP capability and require only the DSM Modbus Exporter software to configure all the DSM inputs and define the Modbus interface.

As always, it is recommended to contact your local Bently Nevada Services group team to assist with this operation. They will be able to help you ensure that the additional information you receive is accurate, optimized and reading correctly. For example, did you know that you can export the alarm set points via Modbus too? Doing so allows you to associate the trended variable with its associated alarms – so if the monitor gets updated, the DCS does too (no more mismatches!!). While the service technician is there, they can also help check out the transducer systems and other components too!

Where Do I Go From Here?

If you are already trending the data mentioned above and you find yourself craving MORE … then it’s time you start looking into System 1. When combined with GE’s advanced hardware, sensors, and portable data collection devices, System 1 helps you to analyze and diagnose the assets across your plant in real-time.

The software provides access to not only the instrument-calculated variables, but many more software calculated variables too. Along with high resolution trend, alarm, & startup/shutdown data, System 1 also stores short-term "black box" flight recorder for deeper analysis during alarm and transient events.

Furthermore, System 1 allows for the collection & analysis of dynamic waveforms, allowing for the use of best-in-class Anti-Friction & Hydrodynamic Bearing Diagnostics to provide deep insights into “why” the machine is behaving as it is.

Be sure to contact your local sales representative to find out more!

Hardware Capability Summary

  Protection Modbus 4-20mA

System 1

3500 + + + +
ADAPT + +   +
1900/65A + + +  
2300 + + + +
TDISecure   +   +
Trendmaster   +   +
vbOnline Pro   +   +

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