RECIP TIPS: Cylinder Pressure Transducer Installation Pitfalls

Cylinder pressure measurements are at the heart of effective condition monitoring for reciprocating compressors. Such transducers provide the all-important pressure-volume (PV) measurements needed to assess mechanical and thermodynamic performance of the cylinder and other parts of the machine. Since this is the part of the machine where compression actually takes place, accurate information is vital in order to ensure the machine is operating with maximum efficiency.

The single most common problem encountered in the field is improper installation of these transducers. When not installed correctly, pressure resonances can occur across the face of the transducer, leading to a transducer output that is completely overwhelmed by the high-amplitude resonance response. The effect is similar to blowing across the mouth of a bottle to create a musical note. If blown just right, the bottle will resonate, often quite loudly.

An in-depth applications note (http://www.gepower.com/prod_serv/products/oc/en/orbit/downloads/ger-4273.pdf) has been developed to assist users in understanding this phenomenon and in designing a proper installation to preclude resonance problems.

 

Brian Howard

Field Applications Engineer, Reciprocating Compressor Condition Monitoring

GE Energy

brian.howard@ge.com

 

 

Recip Tips – Mechanical Protection for Cylinder Pressure Transducers

Cylinder pressure measurements provide critical information about the condition of reciprocating compressors. Such transducers provide the all-important pressure-volume (PV) measurements needed to assess mechanical and thermodynamic performance of the cylinder and other parts of the machine. For reciprocating compressors, the internal cylinder gas pressure generates forces on the piston rod and these forces are typically larger than combined effects from inertia loads, rotating imbalance, etc. Accurate information about the cylinder gas compression cycle provides critical insight into the machine’s running condition and the operating stresses experienced by the various compressor components.

Although data provided by these transducers can be used to greatly improve machine safety and reliability, it is imperative that the installation provides adequate structural bracing of the transducers and associated isolation valves. Failure to install such bracing introduces a very serious safety hazard because if a transducer or valve were to break due to improper installation or physical abuse (see Figure 1), gas would be vented directly to the atmosphere. Indeed, the suction valves in the cylinder will allow all available gas in the bottles, coolers, and piping to vent to the atmosphere even if Operations were to immediately isolate the compression system at the instant the breakage occurs. When hazardous or flammable gases are used, as is often the case with reciprocating compressors, the consequences are even more serious.

Adequate structural bracing safeguards against this in two ways:
1.  It provides additional stiffness that helps reduce effects of vibratory resonance and the potential for fatigue-induced failures.
2.  It provides an additional layer of mechanical protection, guarding the pressure transducer and isolation valve from the accidental impact of an overhead crane hook, dropped tools/parts, a worker’s boot stepping in the wrong place, or similar scenarios.

Figure 1 shows the damage that resulted from an overhead crane hook contacting a cylinder pressure transducer. Fortunately, the primary diaphragm remained in the valve so no release of gas occurred. Further, the bracing extended to the isolation valve so it remained in place and allowed plant personnel to immediately isolate the damaged diaphragm from the internal cylinder pressure.

Figure 2 shows a design for an adequately braced cylinder pressure transducer. At a minimum, the bracket should be designed to have a first mode resonance above 100X running speed. This usually requires the plate be 0.50” [12mm] thickness or greater. Substantial bolts (½” nominal size or larger) should be used to secure the bracket to the cylinder body.

For a detailed design specific to your application, contact local GE sales professional specializing in Bently Nevada* asset condition monitoring products and services.

Brian Howard, P.E.
Field Applications Engineer,
Reciprocating Compressor Condition Monitoring
GE Energy
brian.howard@ge.com

 

Who’s Number One in Vibration Monitoring? CONTROL Magazine Readers Say “GE”

For the 16th consecutive year, GE’s Bently Nevada* product line has won the Readers’ Choice Award in CONTROL magazine’s vibration instrumentation category. The awards, published in CONTROL’s January 2008 issue, are based on a poll of the magazine’s readers who are asked to name the top providers of products and services in a wide variety of categories.

Unlike awards where readers are asked to pick from a list of names, the CONTROL awards are different: readers are given only the category’s name (such as programmable controllers), and they must then write in the name of the provider that they believe to be the leader.

A GE official said “we are honored to be recognized in this way—particularly because the award is based on feedback from a large cross-section of customers, rather than a small editorial staff”.

You can read the complete article, along with results from the 2004-2007 Readers’ Choice Awards, by visiting CONTROL magazine’s website at www.controlglobal.com

 

Compact, panel-mount GE Tachometer is ideal for local or remote speed indication

Highly accurate indication of rotational speed is a fundamental instrumentation requirement for many machines. Tachometers using a 4-20mA input signal are rarely capable of providing the necessary accuracy or resolution; instead, tachometers accepting a pulse-train signal from a once-per-turn or multiple-event-per-turn transducer are preferred due to the superior resolution and accuracy this type of input signal can provide.

For more than 35 years, the Bently Nevada* product line has featured a variety of stand-alone tachometers as well as tachometer modules used in our rack-based machinery monitoring systems. For the reason noted above, these tachometers are designed to work with a proximity probe input from a once-per-turn shaft discontinuity, such as a key or keyway, or a multi-eventper-turn precision toothed wheel.

One of the most popular tachometer styles over the years has been the 37506A, a small panel-mount indicator with a large, easy-to-read display. Customers continue to find many applications for the 37506A, but it is becoming increasingly difficult to support due to the diminishing availability of certain parts. The goal was to provide an updated tachometer that retained the same physical dimensions and functionality as the 37506A, but with updated electronics. The new Tach100 is the result.

The Tach100 is designed to support the same applications as the 37506A, such as stand-alone scenario when speed indication is required locally at the machine, or at a remote location such as a control room. Another very common application of the tachometer is when speed indication is required in two separate locations simultaneously.

Often, a monitoring rack with an installed tachometer will already be available in one location, such as a control room or instrument shelter. The Tach100 can be installed in parallel with the monitoring system, sharing the same transducer input signal, but providing speed indication in a secondary location, such as the machine’s control panel.

Key Features

• Compatible with newer –24Vdc proximity transducers 1, 2

• 1 rpm resolution with improved accuracy (+/- 0.15% of true RPM)

• Front-panel adjustment of trigger levels and event-per-turn settings

• Same physical dimensions as 37506A, making retrofits simple

• Compatible with 37506A accessories, such as hood to block direct sunlight and weatherproof housings for outdoor installations

Additional information and diagrams showing typical installation scenarios are available in the Tach100’s datasheet. You can obtain a copy by contacting your nearest GE Energy sales professional specializing in Bently Nevada Asset Condition Monitoring Equipment, by using the Reader Service Card in this issue of ORBIT, or by accessing the online version of the Reader Service Card at http://www.gepower.com/prod_serv/products/oc/en/orbitmagazine.htm

 

*Denotes a trademark of the General Electric Company.

1 When retrofitting systems using older +15Vdc tach drivers, contact your local sales professional for assistance. These applications require upgrading the transducer system to newer –24Vdc technology.

2 When retrofitting systems using older –18Vdc proximity probe technology, a voltage adapter is available that converts –24Vdc transducer power to –18Vdc.

 

Torsional Vibration Signal Conditioner – TK17 by GE Energy Bently Nevada Line

The TK17 Torsional Vibration Signal Conditioner measures torsional vibration by electronically processing the signals from up to two proximity transducers. These transducers are located on opposite sides of the shaft and observe a precision machined, toothed wheel attached to the shaft.

The two-input feature of the TK17 minimizes radial vibration that may be present at the location of measurement and provides effective noise reduction. Each time a tooth passes under a probe, its output signal changes, producing a pulse. Without torsional vibration, the pulse rate of the probe is a constant. The probe signals are connected to the instrument for conditioning. The TK17′s circuitry sums both input signals and provides one output in units of volts/degree, ready for further processing using standard diagnostic equipment. For single channel applications, the probe signal should be connected to both TK17 inputs.

The signal conditioner accepts inputs from displacement transducers and optical sensors. Both transducers typically observe teeth at a gear. Additionally, the optical sensors may observe reflective tape with contrasting bars. The use of this tape is recommended as a temporary solution in cases where no gear wheel is available.

Specifications

Inputs

Power Requirements:

115 Vac, rated from 105 to 125 Vac; or

220 Vac, rated from 200 to 240 Vac; 50/60 Hz.

Signals:

Minimum peak-to-peak voltage of 2.0 volts.

Maximum peak-to-peak voltage of 28 volts.

Machine Speed:

Minimum 400 rpm.

Maximum 20,000 rpm.

User selectable full-scale rpm of 4,000; 10,000;

15,000; or 20,000; selectable at front panel.

Events per shaft revolution:

20 to 199, selectable at front panel.

Range of Torsional Vibration:

0.1 degree peak-to-peak to 2 degrees

peak-to-peak.

Number of Events:

Maximum events/minute of 1.5 million

(75 teeth at 20,000 rpm, or 200 teeth at 7,500 rpm

are two examples).

Minimum events/minute of 8,000

(20 teeth at 400 rpm).

Output

Signals:

An analog signal representative of torsional vibration,

scale factor front panel selectable at 0.5, 1.0, 2.0, or

5.0 volts per degree.

Maximum Detectable Frequency of Torsional Vibration:

(Shaft rpm) × (events-perrevolution) × (0.0053),

Expressed in Hertz, or 500 Hz, whichever is smaller.

(Increasing events per revolution increases resolution

and range of detectable torsional vibration. Therefore,

it is desirable to maximize events per revolution.)

Physical

Size

Height:

89 mm (3.5 in)

Width:

216 mm (8.5 in)

Depth:

279 mm (11 in)

Weight:

2.7 kg (6 lb)

 

Ordering Information

Torsional Vibration Signal Conditioner (TK17)

100279-AXX

A: Power Input Option

0 1 115 Vac; 50/60 Hz

0 2 220 Vac; 50/60 Hz.

 

Optical Pickup Sensor for Asset Condition Monitoring

When a machine develops problems that require use of diagnostic and analytical equipment, a Keyphasor® signal becomes necessary. For those machines that do not have permanent Keyphasor transducers installed, a temporary Keyphasor or optical pickup is the next best choice. It enables you to obtain timing and phase reference data to perform balancing and diagnostics on rotating machinery.

Copy and pase this url to the browser to gather more information on optical sensors gepower.com/prod_serv/products/oc/en/bently_nevada/case_expan.htm

The optical pickup observes a once-per-turn event marker on the shaft. It generates a voltage pulse that becomes the timing and phase reference signal for speed, phase angle and frequency measurements. These measurements enable you to correlate the instantaneous dynamic motion of the shaft at various points on a machine train and obtain the following balancing and diagnostic information:

• Once-per-turn event marker for RPM measurement.
• Vibration waveforms and orbits.
• Phase angle measurements for balancing. The optical pickup, used in conjunction with our Digital Vector Filter 3 (DVF 3) or ADRE® System, can give a direct shaft reference for phase angle measurements. The ability to obtain direct shaft reference eliminates the need for a trial run.
• Polar plots using the Keyphasor reference pulse for phase angle measurements on a DVF 3 and ADRE® System.
• Bode plots, using a DVF 3 or ADRE System, for showing rpm versus phase and amplitude of shaft vibration.

The optical pickup consists of an LED optical sensor mounted in a stainless steel case. A 3 meter (10 feet) integral cable is attached to the case. If more cable is required, an extension cable can be ordered.

An optical pickup mounting package, which may include a magnetic base, lock grip pliers and flexible gooseneck with holder, is also available.

The optical pickup should be used with our TK15 Keyphasor Conditioner and Power Supply or the DVF 3 (see individual product data sheets). These two instruments provide power and condition the optical pickup signal for use with diagnostic instruments.

Specifications

Electrical

Rise Time: 1 us typical.

Fall Time: 15 us maximum.

Recommended Gap: 25 to 100 mm (1.0 to 4.0 in) observing a 25 mm (1.0 in) wide reflective tape.

Environmental Limits

Operating Temperature: 0°C to +75°C (+32°F to +167°F).

Humidity: To 95%, noncondensing.

Ordering Information

10798-03 Optical Pickup

Extension Cable

20545-AXX

A: Cable Length Option

Order in increments of 1.0 foot (0.30 metres)

Minimum Length: 10 feet (3.0 metres)

Maximum Length: 99 feet (30 metres)

Example: 3 0 = 30 ft (9.1 m).

Accessories

Optical Pickup Mounting Package

20211-AXX

A: Accessory Options

0 1 ¼-20 UNC magnetic base and flexible gooseneck and holder.

0 2 Lock grip pliers with ¼-20 UNC mounting hole and flexible

gooseneck and holder.

0 5 ¼-20 UNC magnetic base and lock grip pliers with ¼-20 UNC

mounting hole and flexible gooseneck and holder.

 

Vibration Meter/Tunable Filter TK81 from GE Energy

The TK81 Tunable Filter/Vibration Meter is a portable handheld instrument for basic vibration measurements. It can display vibration in both unfiltered (overall) and filtered modes. It accepts inputs from displacement, velocity, and acceleration transducers but does not provide power for them.

Its filtering capability is particularly useful for diagnosing vibration problems occurring at particular frequencies on all types of machinery.

Specifications

Inputs

Signal:	Accepts displacement, velocity, or acceleration.
Maximum Input:	10 V peak-to-peak.
Scale Factor:	Selectable from 5 to 9999 mV per engineering unit.
Input Impedance:	95 k W.

Signal Conditioning

Frequency Response:	1.66 Hz to 1,666 Hz (100 to 100,000 RPM).
Integration:	Single integration is available for frequencies above 10 Hz (600 RPM).

Filter

Operating Range:	1.66 Hz to 1,666 Hz (100 RPM to 100,000 RPM).
Type:	Digital, approximates an analog filter with a Q of 11.

Outputs

Display:	4 line by 16 character LCD
Display Units:	Selectable Metric or English,peak-to-peak, zero-to-peak, or rms**.** RMS readings may fluctuate @ < 10 Hz (600 RPM).
Accuracy: Within 5%Within 10%	* Non-Filtered, Non-Integrated Signals @ Full Freq Range* Non-Filtered, Integrated Signals @ 10-16.67k Hz (600-100k RPM)* All RMS Measurements* Filtered, Non-Integrated Signals @ Full Freq Range* Filtered, Integrated Signals @ 10-16.67k Hz (600-100k RPM)

Power Requirements

Battery:	9-Volt alkaline transistor battery. (NEDA 1604A).
Battery Life:	20 hours nominal.

Environmental Limits

Operating Temperature:	+0°C to +40°C (+32°F to +104°F).
Storage Temperature:	-20°C to +70°C (-4°F to +158°F).Note: A battery stored above +104°C(+219°F) or below 0°C (+32°F) will have a reduced shelf life.
Relative Humidity:	To 90% noncondensing.

Physical

Size:
Height:	191 mm (7.5 in)
Width:	102 mm (4.0 in)
Depth:	58 mm (2.3 in)
Weight:	316 g (0.7 lb)

Ordering Information

80649-01

TK81 Tunable Filter/Vibration Meter

Option Description

Includes:

1 TK81

1 9200-09-01-01-00 Velocity Seismoprobe®

1 Seismoprobe® Cable and extension rod

1 Magnetic base

1 Soft carrying case

1 Manual

2 Batteries (1 spare)

Accessories

80466-02	TK81
88737-01	User Manual
9200-09-01-01-00	Velocity Seismoprobe®
7989-01	9200 Velocity Seismoprobe® Extension rod
46000-01	Magnetic Base
46122-01	Quick Connect
80705-01	Interconnect Cable
04160151	Soft Carrying Case
04160152	Strap
03282910	Foam insert

 

GE Energy Launched Wireless Condition Monitoring Solution

GE Energy has launched its wireless condition monitoring system, the Bently Nevada wSIM (Wireless Sensor Interface Module). The wSIM is designed for the non-critical assets which require frequent periodic monitoring. The wSIM provides accurate & reliable temperature & vibration measurement for inaccessible assets, due to remote locations & hazardous environments. The wSIM can be operated using either a battery or a self powered “energy harvester”, which generates power from the vibration motion of the machine itself.

Apart from reducing the cost & time of installation, the Bently Nevada wSIM minimizes human error by enabling plants to gather accurate & reliable data at regular intervals. It takes measurements at programmed intervals & broadcasts the data to “System 1”, GE’s condition monitoring software platform, which performs trending & analysis and provides information for predictive maintenance.

Today there is a need for easy-to-deploy, highly reliable alternatives to conventional hardwired condition monitoring systems. This new technology will make permanent condition monitoring more affordable and practical for a larger percentage of the assets.

For more information on wSIM Click here.