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Using Resistance Measurements to Test and Verify IEPE Accelerometers

Ask the Expert:
Using Resistance Measurements to Test and Verify IEPE Accelerometers

Question:
I want to use Endevco® model 8510B piezoresistive pressure transducers to measure the profile of a small, fast-acting gas valve, such as those used to control air or nitrogen within HVAC applications. The valve pressure profile changes very quickly, almost like a step change. Transducer rise time response is not specified on your product datasheet. Can this product measure fast rise times? How can I accurately calculate rise time response?

Answer:
Yes, the model 8510B (and the entire Endevco® 8500 pressure transducer series) can measure extremely rapid rise time pressure pulses. Meggitt does not specify rise time response on the product datasheet. Instead, we specify sensor resonance frequency. This allows the user to apply general dynamic measurement “rules-of-thumb” to calculate rise time response, given that the pressure transducer itself can be approximated as a single degree-of-freedom mass-spring mechanical system with practically no damping.

To further illustrate, the “period” of the sensor is simply the reciprocal of the resonance frequency specification:

In order to remain within the linear region of frequency response, it is recommended to use no more bandwidth than 1/5 of the total sensor resonance frequency. This bandwidth is the “flat” region of sensor frequency response.

Thus, the above equation becomes:

Now, from Fourier analysis, it is well known that rapid rise time pulses contain high-frequency content. In order to avoid exposing the sensor to these high frequencies (to prevent distortion and signal overshoot), it is recommended that the transducer’s period be 1/4 to 1/2 of the expected rise time, or:

By solving for T and substituting into the previous equation, we arrive at:

So, given a sensor resonance frequency specification, we can now accurately calculate pressure transducer rise time response.

For example, the Endevco® model 8510B-500 has a specified resonance frequency of 500 kHz. Using the above equation, the rise time response would come out to:

In addition to the HVAC related application example highlighted here, the Endevco® model 8510B series may also be used to effectively support the pressure monitoring requirements of wind tunnels, blast and ballistics, hydraulics systems, wave studies, chemical reactors, and automotive airbag and transmission safety testing.

For more information about the products available from Meggitt Sensing Systems, visit meggittsensingsystems.com or www.TALON.biz

Posted in Industrial Automation, Physical Measurement, Principal News, Sensors.

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By Jack Hunter – March 16, 2012

Fluid Level Alert for Safety and Control

PMCWe are delighted to announce a new Water Level Warning System based on our Precision Level Transmitters.

Lev-Alert was developed at the request of one of our existing customers and has already proven to be fully justified in both industrial or office environments. It can also be configured for pressure, RH or temperature related installations.

The PMC Lev-ALERT can provide visual or audio warnings when the fluid/water/sewage reach dangerous levels. It also provides switch outputs to control appropriate output pumps or input valves.

More Lev-Alert Product Information

Posted in Physical Measurement, Principal News, Sensors.

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By Jack Hunter – March 16, 2012

High Pressure Transducer

PMC

The VB series has been designed specifically for those applications where very high pressures up to 36,000 psi are to be measured, and temperatures might be as high as 400ºF. Typical applications range from oil field instrumentation, including MWD down hole, to turbine engine monitoring. The performance is achieved by using the very latest processes in thin film strain gauge techniques and is offered without any active amplification or compensation. The VB2100 shown above, is a specific example offering small size and fast frequency response through the flush diaphragm. This has been a specialty of PMC for more than 40 years. The technology is available in a number of different configurations, and we invite potential customers to contact our technical staff at the factory for any required customization.

Series VB 105 2.27.12 Data Sheet

Posted in Principal News, Sensors, TALON News.

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By Jack Hunter – February 28, 2012

2010 Subsea Tieback Forum & Exhibition

Join Hoffer Flow & TALON at Booth A12

The annual Subsea Tieback Forum & Exhibition has become the premier event for one of the fastest growing sectors of the oil and gas industry. This year’s Subsea Tieback is scheduled for March 6-8, 2012 in Galveston, TX at the Moody Gardens Hotel & Convention Center. Over 3,000 attendees and 200 exhibitors are expected at next year’s conference. You can’t afford to miss it.

This year’s theme is “Learning From Adversity.” As our industry changes, the sharing of knowledge and collective experiences becomes more and more crucial to improving the quality, safety, and economics of the subsea tieback industry.

The conference board will once again solicit a number of key presentations by industry leaders. As in the past, only by participating in this conference will you be able to receive its benefits, as proceedings will not be published and no Press is ever allowed in the conference area. This is truly a closed forum with open discussion, where the information shared inside the conference room stays inside the conference room. We hope you will join us in Galveston for the 2012 Subsea Tieback Forum & Exhibition.

CLICK HERE for more information.

Posted in Principal News, TALON News.

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By Jack Hunter – February 22, 2012

Ask The Expert


Ask the Expert:
Using Resistance Measurements to Test and Verify IEPE Accelerometers

Question:
We have installed several Endevco® (IEPE) accelerometers within our test structure. Is it possible to use resistance measurements to check whether they are wired correctly? Can you recommend how to properly verify accelerometer functionality?

Inside IEPE:
Integrated electronics piezoelectric, or IEPE, accelerometers are offered by Meggitt under the trade name of Isotron®. Their distinguishing feature is their integral electronic impedance converter, which eliminates the need for an external charge amplifier. Their integral electronics are compatible with the same industry standard IEPE current sources built into many FFT analyzers and data acquisition systems. They can also drive long cables with minimal noise distortion and pick-up.

Figure 1 shows the basic configuration of a case grounded IEPE accelerometer.

As illustrated in Figure 1, the lower side of the piezoelectric crystal is connected to the case, while the upper side (hot side) is connected to the mass. The charge output of the crystal is connected internally to the charge amplifier input. The charge amplifier output is brought out to the connector pin as the main accelerometer output. Available lines for resistance measurements are both the IEPE output and the signal return line, also known as the common line.

Answer:
An ohmmeter may be used to detect whether wiring is shorted, open or whether there is gross isolation failure.

A low-voltage ohmmeter can be connected at both the IEPE output and the signal return line. Resistance measurements between the IEPE output and the common line can detect dead short, in which case, resistance is practically zero. They can also detect open circuit conditions, which have extremely high resistance. If the accelerometer’s signal return is isolated from ground, resistance measurements between the signal lines and the shield ground can also detect gross isolation failure if the resistance reading is low. Please also note that any readings between the IEPE output and the common line will most likely indicate that the wiring between them forms a complete circuit.

An ohmmeter cannot be used to directly verify IEPE accelerometer functionality.

In good working IEPE accelerometers, resistance readings can vary widely and may exhibit diode effects, particularly within those accelerometers that are further equipped with Transducer Electronic Data Sheet (TEDS) capabilities. For example, one polarity that reads 50,000 ohms may read 350 ohms in reversed polarity (reversing the ohmmeter test leads). These readings are neither consistent nor repeatable unit-to-unit, even within the same lots of accelerometers. In addition, the selection of ohmmeter type, such as analog or digital, typically accounts for wide variations in reading results. The reason for such variations is that the physical parameter measured by the ohmmeter is resistance of an unbiased output active device of the charge amplifier output stage. As such, it is not possible to reliably test IEPE accelerometer functionality using resistance measurement methodologies.

Testing IEPE accelerometer functionality:

The only true and reliable means of testing IEPE accelerometer functionality is to power up the accelerometer using a constant current source, such as the Endevco® model 4416B, or typical setup, as shown in Figure 2. Once the constant current source is applied, measurement of the quiescent bias voltage across accelerometer lines allows for an accurate check as to whether the voltage reading is in specification. The bias reading of 0-2 Vdc indicates a bad output stage, while bias reading of 20-24 Vdc (with 24 Vdc compliance voltage) indicates a bad input stage. In addition, if there is a means of physically tapping the accelerometer within this setup, the output signal from the “tap” can be monitored using an oscilloscope. A pulse can be observed at the oscilloscope display while the accelerometer is being tapped. For very low output accelerometers, the input vertical gain of the oscilloscope may need to be increased until the output is viewable.

For more information about the products available from Meggitt Sensing Systems,
visit meggittsensingsystems.com

Posted in Industrial Automation, Principal News, Sensors.

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By Jack Hunter – February 22, 2012

Customizable SG1 Provides 80-inch Stroke Range, IP67 Protection and


Chatsworth, CA ~ Celesco Transducer Products is now selling the SG1 – a slim, compact and low-cost stringpot that is now in stock, available for immediate delivery and can be completely customized to meet the specific needs of OEMs.

The SG1 ships with a 10K-ohm potentiometer that provides a voltage divider output signal proportional to the position of the spring loaded measuring cable. The SG1 is designed to not only meet the needs of OEMs and single piece users, but is also receiving rave reviews as an off-the-shelf sensor. It has a stroke range of 80 inches and will soon offer a 120-inch stroke version. This compact, low-cost sensor can be easily installed using the handy mounting bracket.

The SG1 is constructed with a rugged polycarbonate body, a precision high-cycle plastic hybrid potentiometer and a durable spring-loaded stainless steel measuring cable. The SG1 has been designed for tight spaces, complete with a generous measuring cable misalignment and free release tolerance. Its measuring cable provides an accurate reliable position feedback signal over the entire stroke.

Available electrical connection options include the popular M12 connector, a 40-inch pigtail or solder terminals directly on the SG1 pot. To withstand wet IP67 environments, the M12 connector and pigtail options provide a rugged O-ring sealed cover to protect the potentiometer against the elements. Additionally the M12 connector option comes with a field installable mating plug and an optional 13-ft. cordset is available.

The SG1s ability to be customizable for OEMs really sets it apart. Such possibilities include a choice of connectors, custom designed mounting hardware and even a choice of potentiometers or other output signals. It is an ideal stringpot for customers searching for a low cost sensor for their application.

The SG1 has been designed to fit into spaces no other measurement device can, said Celesco General Manager Jim Bishop. Its simple to use and very flexible. We feel it is the perfect of-the-shelf economical solution for both the OEM and single piece user.

Other key applications and benefits of the SG1 include:
• Low cost, in stock and available for immediate delivery
• Stroke range of 80 inches (2,032 mm)
• 0.35% Linearity
• Operating temperature of 0 to 160 degrees Fahrenheit
• IP67 environmental protection (M12 and electrical cable option)
• 10K ohm, plastic-hybrid precision potentiometer sensing element
• 9 oz. (2,5 N) measuring cable tension
• Electrical connection via solder terminals, 40-inch electrical cable or M12 connector
• Handy mounting bracket that lets the user mount the sensor in just about any direction.

…Datasheet

Posted in Industrial Automation, Physical Measurement, Press Release, Principal News, Sensors.

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By Jack Hunter – February 2, 2012

MODULAR RE-CONFIGURABLE OPERATOR CONTROL UNITS AND SYSTEMS

Bokam Engineering

• Modular System consisting of standard building blocks configurable to meet application requirements
• Fully integrated and multi-part OCU configurations available for all in one or distributed box configurations
• All proportional input devices are solid state with life expectancy over 10,000,000 life cycles.
• Fully programmable and user re-programmable input device functionality make each device either a proportional inputs, buttons, toggles or multi function inputs.
• Thin walled sealed aluminum structure provides exception shock resistance, shielding and great thermal qualities in light weight package.

• Water tight packages for superior seal and survivability
• Specially treated aluminum coatings provide superior scratch resistance and range of colors.
• Rubberized removable Side Grips allow for comfortable hold and straps for extra security
• Up to 10 Two Axis Solid state Position or Force Proportional input Devices –
programmable as proportional controls, toggles or multi position buttons and 8 push
Buttons and up to four proportional triggers
• Various size day light readable and touch screen display options available
• Various computing options allow for processing power to be customized to specific needs
and budgets.
• Add-on radio Module with various frequency ranges and functions

… more

Posted in Industrial Automation, Sensors.

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By Jack Hunter – February 2, 2012

Wilcoxon Research products – now with Lifetime Warranty!

Germantown, MD –– Meggitt, a leading supplier of quality vibration sensors and sensor networks, has announced the offering of LifeTime Warranty (LTW) on Wilcoxon Research sensors and accessories. By launching one of the best warranties in the industry, Meggitt is providing a statement of trust and reliability to strengthen its customer relationships.

LifeTime Warranty is available on popular Wilcoxon products serving a wide range of applications to ensure lasting customer relationships through Meggitt’s commitment to product quality and customer service. The combination of Meggitt’s LifeTime Warranty and Guaranteed InStock program gives customers 100% product satisfaction, quality assurance and decreased lead time. Providing the highest levels of service with 50 years of vibration monitoring expertise make Wilcoxon Research products the industry standard in many plants worldwide. “Customers expect a higher standard from us” said Tom Smith, VP of Sales and Marketing of Wilcoxon Research products. “Adding LifeTime Warranty to our trusted product lines and providing the best service shows that we are truly committed to customer satisfaction.”

Wilcoxon Research products are developed with a superior design technique that leads to better overall performance and quality. All accelerometers follow the hermetically sealed, ESD protected and EMI/RFI shielded construction that has made Wilcoxon sensors the choice for many maintenance professionals worldwide. Long product lifetime ensures that vibration monitoring programs will continue uninterrupted and failure free.

“Meggitt’s confidence in the performance of Wilcoxon Research sensors drove the decision to introduce LTW” stated Derek Carbin, General Manager of Wilcoxon Research products. “Wilcoxon sensors are known for performance and reliability, adding LTW will reinforce their reputation as the products with the highest standard in the industry.” Wilcoxon Research product lines that will be covered under LifeTime Warranty include most industrial accelerometers, 4-20 mA vibration sensors, cable assemblies, connection/switch boxes, and mounting accessories. To learn more about Wilcoxon Research products, Meggitt Sensing Systems, or LifeTime Warranty, visit www.talon.biz, call 281-999-8588, or email info@talon.biz.

Posted in Press Release, Principal News, Sensors.

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By Jack Hunter – January 16, 2012

Depth/Level Transmitter – side entry cable – VersaLine VL4563 Series

PMC has engineered  a  rugged side entry cable to facilitate the use of their submersible transmitters inside pipes  where the level measurement is required under flowing conditions.  This is offered as a standard option for “¾” inch diameter  transmitters but can also be provided for other series. The combination of the low profile Transmitter and the side entry cable are ideally suited for installations into sewer pipes to minimize flow restrictions and possible clogging.

The design is very much focused on installations in sewer pipes where, taking advantage of the low profile of the VL4500 series, it is placed at the bottom of the pipe and the cable is attached via a strap to the surface. Our pilot installation for this feature has been in New Zealand where we now have more than 100 installed with 100% success and customer satisfaction. The molding, contained within the titanium housing follows are standard process for polyurethane cable. VL4563 side entry cable 10132011

 

Posted in Industrial Automation, Physical Measurement, Press Release, Sensors.

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By Jack Hunter – October 13, 2011

PMC Expands the VL3000 range to Include SDI-12 Protocol

PMC

These submersible transmitters are specifically designed for depth and level measurements of groundwater, wastewater, and sea water. Typical applications are wells, dams, irrigation, sewage lift stations, rivers and oceanography. The stainless steel housing will satisfy many applications. Titanium is also ideal in brackish or sea water, or other chemical environments unsuitable for stainless steel. The standard polyurethane vented cable is molded to the transmitter providing the highest integrity waterproof assembly well proven in thousands of installations worldwide. Kevlar is used to avoid any cable elongation when longer lengths up to 5000 feet are required for deep wells.

It should however be noted that when using SDI-12 protocol the cable length can be limited by the number of transmitters on the same line. For example the current SDI-12 specification states that – “the bus is capable of having at least 10 sensors present each with 200 feet of cable on each sensor”. We can also confirm that when a single transmitter is used cable lengths of up to 500ft are acceptable. For really long lengths up to 5000ft PMC recommends the VL4500 series with 4-20mA output. FEP cable is available as an alternate for harsh environments. A feature of the VL3004 Series are full scale ranges as low as 20” WC.

Data sheet for VL3004 109a SDI-12

Posted in Physical Measurement, Principal News, Sensors.

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By Jack Hunter – October 6, 2011