All You Ever Wanted to Know About Online Protection Systems

All You Ever Wanted to Know About Online Protection Systems – Part 2

Panel Monitor Systems

As I mentioned in Part 1, a machinery vibration protection panel system comprises:

  1. Displacement probes (‘probes’) & coaxial cables (which connect to the proximitor)
  2. Proximitors (or ‘Drivers’ or ‘Oscillator / Demodulators’)
  3. Field Wiring – to / from the proximitors to the Zenner Barriers
  4. Zenner Barriers
  5. Rack (Housing) System
  6. Panel monitors
  7. Relays to installation DCS system – to provide external alarm annunciation or input to an automatic shutdown device.

The above items (1-3), are located in the “Hazardous Area”, whereas items (4-7) are installed in a “Safe Area”.

There are a number of different types of protection panel monitors, which can be installed within your rack system e.g.:

  • Dual channel radial probe monitors
  • Dual channel axial probe monitors
  • Multi-channel temperature monitors
  • Reciprocating compressor rod-drop monitors
  • Keyphasor monitors

However, in this article, and for the sake of brevity, reference will only be made to radial probe, axial probe and keyphasor probe monitors.

Rack Components

A typical protection panel system comprises the following items:

  • A Rack (or housing) – to accommodate the undernoted modules
  • A power supply – to provide power to the monitors in the rack
  • A system monitor
  • Vibration monitors – for displacement, velocity & acceleration
  • Keyphasor modules

The above are only a representative list of monitors that are available, and a range of other monitors/modules are available used for a range of different requirements.

The Rack

The rack, which is normally 19” (482.6 mm) is the part, which ‘houses’ the individual monitors. They have a backplane with multi-pin connectors attached for each individual monitor to connect to. Each rack must accommodate the Power Supply, System Monitor and various types of monitor. The images below show an old style Bently Nevada 7200 Series and 3300 Series monitor racks, with the newer style of rack shown below these 2 images.

Bentley Nevada 7200 Series Rack System Bently Nevada 3300 Rack System Sensonics G3 Protection Rack System


The power supply

The power supply is itself powered from the platform or installation’s power supply system (i.e., a 240 V or 110 V ac supply, or a DC supply). This in turn, supplies power to each of the rack monitors and their associated transducers. It converts the input AC power into DC voltages used by the monitors installed in the rack. The power supply can provide either – 24 V dc or – 18 V dc voltages to each monitor for powering the attached transducers. The transducer voltages are overload protected, per channel, and on the individual monitor circuit boards. Each manufacturer stipulates where the power supply module must be located in the rack – either the first or last (depending on manufacturer) module – working from left-to-right.

The rear panel of a Sensonics G3 rack system is shown below, provides terminals for connecting the primary (input AC or DC) power, Rack Inhibit Control, Trip Multiply Control, Remote Alarm Reset control, and two keyphasor transducers, and connections for communications processor, optional serial interface for communications with PLC’s, SCADA systems and DCS systems, and includes terminals for OK relays.

Rear Panel Sensonics G3 Rack System

The System Monitor

A system monitor can provide:

  • Alarm setpoint adjustment
  • Keyphasor power, termination, conditioning and distribution
  • Alarm acknowledgement
  • Control of the “OK” function
  • Buffered keyphasor output signals at the BNC connectors on the front panel.

Optionally, it can also provide:

  • Serial Data Interface (SDI) for communication of transducer and monitor data to process computers, digital / Distributed Control Systems (“DCS”). Programmable controllers and other control and automation systems.
  • Dynamic Data Interface (DDI) for communication of transducer and monitor data to compatible Bently Nevada machinery management software (e.g., System 1).
  • The ‘Trip Multiply’ function, which when activated, multiplies the selected monitor’s alarm setpoints by 2x or 3x (this is specified at the time of ordering). This is set for an individual monitor, so you can set which monitor(s) in the rack are to operate with the trip multiply function.

The OK function, mentioned above, indicates the correct operation of the system and associated transducers and field wiring. The system monitor drives the OK relay, which is located on the power input module. If a transducer or field wiring develops a fault, the OK relay will latch and a “Not OK” signal will be annunciated, and the relevant channel OK LED will flash.

The ‘Trip Multiply’ function, which when activated, multiplies the selected monitor’s alarm setpoints by 2x or 3x (this is specified at the time of ordering). This is set for an individual monitor, so you can set which monitor(s) in the rack are to operate with the trip multiply function.

  1. Trip Multiply – between a certain speed (rpm) range, at which there is a ‘critical’. However, when the machine is operating out with this rpm range, its normal alarm levels are in operation.
  2. Inhibit functionality can be used temporarily suppress all alarming. There are various types of inhibit functions. Some such as “Rack Inhibit” essentially disable all functions of the monitoring system – not just alarms. This essentially means ‘running blind’ with no indication of vibration levels whatsoever.
  3. Alarm Time Delays – this can be used to ensure that a channel must continuously be above its alarm setpoint for a pre-determined duration before the alarm will trigger. This option can be useful for machines, which pass very rapidly through a resonance.

The system monitor also must be installed in the rack in a specific rack position (working from   left-to-right).

Dual Channel Radial Probe Monitors

These monitors, depending on the manufacturer and model, may have a monitor meter, which will have two measurement scales: (a) a vibration amplitude scale – normally scaled in microns peak-to-Peak in the UK, and (b) a DC gap voltage scale – in negative volts DC.

This type of vibration monitor meter will either have a pair of analogue meter ‘needles’ (the old 7200 Series Monitors) or an LED bar graph (3300 System Monitors), to indicate each individual transducers overall level amplitude. The DC gap voltage is obtained by means of pressing a dipswitch, below the meter, on the front panel of the monitor. Later models – the current 3500 series system, does not have a direct monitor indication of vibration amplitude levels or of the associated gap voltages, but rely instead on a connected computer or built-in display screen to display the data.

Older Rack & Monitor Types

The older rack monitors have analog gauges with a set of switches and LED’s.

The Bently Nevada 7200 series monitors (see below) are an example of this earlier type of monitor and have a gauge at the top, various LED’s and three separate spring-loaded switches. Below the switches, are the “buffered Output” connectors (4 mm in this case). The ‘blue’ buffered output is for the “vertical” channel, whilst the ‘green’ one is for the “horizontal” channel. However, the transducers, which provide the signal to these buffered output connectors, may not in reality be truly mounted in the vertical or horizontal plane.

The top (centre) switch of these monitors is used to toggle between displaying, on the meter scale, the “Alert” and “Danger” setpoint values, which has been set up in the monitor. The ‘alert’ setpoint will be displayed by pushing the switch to the left, and conversely, by pushing this switch to the right, the ‘danger’ (or “trip”) setpoint values will be displayed on the meter scale. The danger setpoint, when exceeded, will simply stop the machine – hence the term ‘trip’.

The lower two switches are used to display, on the meter scale, either the dc gap voltage (switch pressed down), or the overall vibration amplitude, for the selected channel – switch pushed upwards. These 7200 series monitors normally display the overall vibration level, for the probe with the highest vibration amplitude, between the two vibration channels.

To obtain the DC Gap Voltage for a specific channel, the appropriate lower switch is pressed downwards (i.e., in the “GAP” Parajumpers Jacka Kodiak direction), and the voltage for that probe is displayed on the “Black” (left) scale, by the red needle. To display a channel’s Overall Vibration Level, press the appropriate channel’s switch upwards (in the “VIB” direction), and the vibration level for that channel can be read on the “Red” vibration scale (on the right).

7200 Series Dual Probe Monitor


7200 Monitor Switches & LED

At the foot of each 7200 monitor, there are two 4 mm plug sockets (blue & green above), as previously mentioned, one for each probe channel, which are referred to as “Buffered Outputs”. Each buffered output is used to obtain vibration and gap voltage data from each of the probes, using for example, a portable vibration data collector and / or an analyser, such as an NI ‘Zonicbook’, Bently Nevada ‘ADRE’ unit or an HGL Dynamics.

Note: on the 7200 series monitors, one (Signal) red ‘Banana Plug’ should be connected to the appropriate probe channel buffered output socket, and the black (Common) banana plug should   be connected to the rack System Monitor’s “Common” (Black) 4 mm socket.

In contrast to the old Bently Nevada 7200 series monitor, their newer 3300 Series Dual Radial Probe monitor (which is shown overleaf), has a LED bar graph style indication of vibration and gap voltage levels on their meter scales.

Dual Channel Radial Probe Monitors

The 7200 series dual radial and axial probe meter scales are shown immediately below:

7200 Radial Meter 7200 Thrust Monitor Meter

More Modern Generation Rack & Monitor Types

In the 3300 monitors – shown below, there two BNC ‘buffered output’ connectors, a DC Gap voltage toggle switch, and the two setpoint display switches on their front panel. These monitors, in contrast to the 7200 series ones, display both channels overall vibration levels simultaneously. Therefore the only switch, which would normally be required to be pressed, is the ‘gap’ switch, which displays each channel’s dc gap voltage in the centre scales.

3300 Dual Radial Probe Monitor 3300 Monitor Front Panel

As can be seen from the 3300 Dual Radial Probe Monitor  previously, each of the 3300 series monitor channel’s displays the overall level as an independent bar graph, with each probe’s amplitude level being indicated on the scale on the left and right side of the meter. The meter’s centre scale is used to display the gap voltage for both channels. By default, the 3300 series monitors normally display the overall vibration level for both channels (recall: the 7200 series monitors only display the level for the probe with the highest level – since these monitors only have a single vibration scale). However, in order to display the DC Gap Voltages on a 3300 series monitor, the dipswitch labelled “GAP”, which is located at the foot of the monitor’s front panel, should be depressed. A 3300 dual axial thrust probe meter scale is shown below.

7200 Dual Thrust Probe Monitor 3300 Dual Thrust Probe Monitor 3300 Monitor Scale

In order to obtain the ‘Buffered Output Data’ from a 3300 series monitor, the data collector (or analyzer) should be connected to the BNC buffered output connectors at the foot of the  monitor’s front panel by a BNC-to-BNC cable. In the case of the 3500 monitors (as with the 3300 monitors), no other connections to the rack are required, in order to obtain the vibration and / or gap voltage data (with the exception of phase data – which is obtained from a separate keyphasor monitor).

These monitors (7200 & 3300 Dual Thrust Probe Monitors & 3300 Monitor Scale) mentioned earlier, have a different measurement meter scale to the radial probe monitors (Radial & Thrust Monitor Meters & 7200 & 3300 Dual Thrust Probe Monitors & 3300 Monitor Scale) – in that they have a ‘centre zero’ axial displacement scale.  Above the ‘zero’ mark on their scale, is the ‘positive’ or “Normal” section of the scale, and below the ‘zero’; is what is referred to as the ‘negative’ or “Counter” part of the scale.

These monitors are normally configured in such a way that the meter reading indicates a zero value when the shaft thrust collar is located mid way between the thrust bearings “active” and “inactive” bearing pads.

When the shaft is thrusting in its ‘normal’ thrust direction (i.e., towards the ‘active’ thrust pads), the displacement – usually scaled in mm (or in MIL’s), is shown as a ‘normal’ or positive value on the monitor’s meter. If, on the other hand, the shaft is thrusting towards the ‘inactive’ thrust bearing pads, it is said to be in the “counter” direction – or a negative direction, and the value is assigned in this case as a negative reading value.

Note: these monitor scales are normally marked in millimetres (mm) or MIL’s, since they  are measuring the physical distance (gap) between the probe tip and the shaft thrust collar,  and/or the end of the shaft.

Power Supply / System Monitor Module – Keyphasor Outputs

7200 Series Power Supply 3300 System Monitor

The 7200 Power Supply module is ‘powered’ from a 240 or 110 V ac power supply. This module in turn provides DC power to each of the rack monitors and their associated transducers. It also provides two other main functions:

  • A “common” ground (black) 4 mm socket connector – for ‘grounding’ the buffered output signals for the individual monitor channels (see 3300 System Monitor above).
  • Dual “keyphasor” buffered output signals – for the 7200 power supply, or four in the case of the 3300 system monitor.

In order to obtain the phase angle from this module, connect to the appropriate keyphasor connector (i.e., Kf 1 or Kf 2) and the centre (black) ‘common’ socket.

The 3300 System Monitor on the other hand, has four Keyphasor buffered BNC output connectors on the front panel. The front panel of this module also has two LED’s – one for  Supplies OK –, which is illuminated (green) when the supply voltage is within tolerance. The second LED indicates; when illuminated (green), that the Trip Multiply function is active.

Below the LED’s, there are two adjacent switches for adjusting the setpoint levels up or down. The bottom centre switch is a reset switch. This monitor also provides the power to the keyphasor transducers.

Keyphasor probes provide a once-per-turn voltage pulse – either a negative or positive pulse, depending on whether the keyphasor probe is sensing a notch feature such as a keyway (negative pulse) or a projection such as a key – giving a positive voltage pulse as previously described (see ‘Keyphasor Probes’ from Part 1).

3500 Series Keyphaser Module Sensonics G3 Keyphaser Module

In the case of the 3500 rack system, it has dedicated 2-channel keyphasor modules, which differs from its predecessors (the 7200 and 3300 systems), which in their case were located  in the power supply module and system monitor respectively.

The Rack Interface Module (RIM)

3500 Series RIM Module

This module provides a means of setting up the rest of the rack monitors, has four status LED’s for: OK Relay, TX/RX, TM and Config OK. These LED’s indicate if the RIM is operating properly: (a) when it is communicating with other rack modules, (b) when in trip multiply mode, (c) when the module is communicating, (d) and that the rack has a valid configuration respectively.  Below the LED’s there is a rack ‘reset’ toggle switch.

The RIM module has a “Run / Program” key switch in the centre of the front panel, an address switch, and a D-Type (9-pin male) connector for rack / PC communications.

This module partially replaces the functionality of the system monitor in the 3300 series rack systems.

Modern Rack Systems

Current Generation Rack & Monitor Types:

The current protection system rack systems differ from their predecessors, in that they no longer have an analog meter mounted on their front panel. They may have a display, as shown below in the Sensonics G3 rack, or may be limited to only having a set of BNC buffered output connectors. [Note: the Sensonics has a set of SNB screw type buffered output connectors for each channel.]

Sensonics G3 Rack Sensonics G3 Module

The above monitor is a 4-channel monitor, in contrast to previous monitors, which were 2-channel monitors.  In addition, the above Sensonics G3 monitor can have each individual channel configured; through the configuration software, to be set up as any of the previous monitor channel types. This is because each channel has its own individual PCB, as shown below-left.

G3 4 Channel Protection Module

However, other manufacturers have 4-channel monitors, which are designed specifically for a particular function – see below the Bently Nevada 3500 series monitors.

Bently Nevada 3500 Series Monitor

The 3500 monitors, have 4 transducer channels connected to them, each of which should be identified on the card below the BNC buffered connectors. The four channels are labelled as Channel 1, to channel 4 – reading from top-to-bottom.

Another obvious difference between the 3500 series and the 7200/3300 series monitors, is that the panel of these 3500 series monitors only has a set of LED’s (“OK”,  “TX/RX” and “Bypass”) and the four BNC buffered output connectors.

The Bently Nevada 3500 System is their current system, whereas the 7200 series system is now termed “obsolete” by them and there are no parts available for these. The 3300 series racks are still currently in widespread use, but now with limited spares availability.

However, the 3500 series rack systems, in common with the 7200 and 3300 series racks, must have a power supply. But in the case of the 3500 series racks, they have a Rack Interface Module (“RIM”) instead of a system monitor. The Sensonics G3 rack has a “Comms Module”, which does the same thing.

The function of the RIM is to configure the rack monitors, and retrieve machine information. The RIM must be installed in “Slot 1” – which is the left-most slot position in the rack in the 3500 rack. A RIM monitor image is shown below.

RIM Monitor

In the case of the Sensonics G3 rack, the Power Supply and Comms monitor are both located at the left-end of the rack, as shown below.

Sensonics G3 Protection Rack System