Category Archives: pressure transmitters

flame instability

Pressure Transmitter to Detect Burner Flame Instability

Large-scale industrial installations such as refineries and chemical plants often have large heaters that are used in the processing of fluids and gases.  Such heaters must now be designed to minimize NOX emissions to meet Federal clean air requirements and much research has gone into finding ways to make the burning process more efficient.

The technology to reduce emissions in large-scale heaters is complex, but for gas-fired heaters part of the solution is to run the natural gas feeding the burners at a reduced pressure to allow for more complete combustion.  But running lower burner gas pressures increases  the risk of a flame-out – and restarting a large heater could cost hours of downtime.

A large oil company that was retrofitting low NOX burners into their heaters decided to design a system that would detect the conditions present in the combustion chamber just before a flame-out.  When a burner flame becomes unstable it wobbles – much like a candle flickers just before going out.  Because the burners are enclosed, the air pressure inside the heater will exhibit a characteristic oscillatory behavior just as the flame begins to fail.  The air pressures inside the heater are low – just a few inches of water – and this pressure will vary at a characteristic frequency of a few Hz just before flame-out.

Validyne developed a version of the DR800 that is sensitive enough to detect the low heater pressures, yet responsive enough to capture the pressure waveform prior to a flame-out condition.  The electronics of the DR800 were modified to pass frequencies up to 50 Hz and the damping circuit was bypassed.  The modified DR800 is capable of passing low pressure variations up to 10 Hz with no distortion.  The DR800 is FM approved as an intrinsically safe device for Class I, Div 2, Groups B, C and D hazardous locations and is ideal for this application in oil refineries.

Pressure Transmitter

The customer developed a signal processing algorithm that detected a pending flame-out condition in their burner from the character of the DR800 signal.   This involves analyzing the  signal for the right combination of frequency and amplitude of air pressure that occurs prior to a flame-out.   When this situation is detected, a warning light is displayed on the operators control panel and action can be taken to avoid a flame-out and time consuming restart.

The major refinery operators – Exxon, Chevron, Union, etc – will be able to develop a detection algorithm suitable for each individual heater configuration.   Another potential market is the burner manufacturers such as Zeeco, John Zink and others, who are purveying low NOX systems.

 

 

landfill gas

Low Pressure Transducers to Monitor Landfill Gas

A new source of natural gas is the collection of methane that accumulates in landfills.  Methane accumulation is the result of the natural decay of organic materials that are part of the landfill.  Conventional natural gas wells are thousands of feet deep and produce gas at very high pressures.  The methane gas in landfills occurs at much lower pressures – from just a few inches of water to a few psi.

It is important to measure the pressures that can be sustained by the methane gas in a landfill, and this is done by installing several shallow wells and recording the pressure over time.  The Validyne P55 series of pressure transducers are ideal for this application because of their sensitivity to very low pressures, compatibility with methane gases and a 4-20 mA power/signal cabling that requires just two wires and can be run over very long distances to a central data collection point.  The Validyne low pressure transmitters are available in full scale ranges as low as 0 to 3.5 InH2O for a 4-20 mA signal, with an accuracy of 0.25% FS.  The 410 steel wetted parts and Buna-N o-ring material is compatible with methane gas and many other hydrocarbon fluids.  The P55 is rugged and compact, and is available in a weatherproof NEMA 4 enclosure.

P532 Pressure Transmitter

If after testing a landfill is found to be able to sustain methane gas production, collection and transmission facilities are built on-site to bring the landfill gas into the wider natural gas delivery network.  For permanent installations the Validyne DR800 pressure transmitter is often used as this provides even lower full scale ranges – as low as 0.25 InH20 for a 4-20 mA signal.  The DR800 pressure transmitter also has a NEMA 4 enclosure with conduit connections and a junction box for signal and power wiring.  The selectable damping feature smooths out small variations in the signal to provide for better pressure control.  The DR800 is also available with a Factory Mutual Intrinsically Safe rating for use in hazardous locations.

Differential Pressure Transmitters for Kiln and Furnace Applications

Many industries rely on large furnaces. For example, the gas and oil industry uses a great deal of heat to refine and process crude oil. The steel industry must heat metals as part of heat treatment processes that occur in special furnaces. With new EPA regulations and efficiency considerations, it’s important to keep pressure low and this has led to special draft range differential pressure transmitters like the DR800. This instrument provides several important benefits in furnace operations.

The Importance of Furnace Draft

The flow of air within a furnace is a vital to energy efficiency and heat control. But what is draft? Draft is the difference between atmospheric or room pressure and pressure within the furnace combustion chamber. This affects the flow of airneeded for the combustion process.

Drafts can be natural, forced, induced or balanced. It is important to monitor this airflow at all times, as it can greatly affect temperature and heat transfer. Draft range differential pressure transmitters are able to detect very low amounts of pressure and send their readings to a furnace control system. In fact, the DR800 can measure pressures as low as 0.1 inches H2O full scale, delivering accuracy to within 0.5 percent. The DR800 is extremely stable, even though large ambient temperature ranges.

Thanks to the DR800, pressure calibration is uncomplicated. It is made possible by including a Hi/Lo gain jumper and continuous the span adjust. You also can choose an LCD display for local indication.

The DR800 is very durable, but should you need repairs they can be done right in the field. You can easily remove its entire electronics housing without disassembling the unit. Plus, your maintenance personnel won’t have to carry specialized tools for the job. The NEMA 4 enclosure and standard process industry form factor make the DR800 easy to use.

To check out the differential pressure transmitters we have to offer, visit our home on the Web today at http://validyne.com/ or call 818-886-8488.

Pressure Measurement in Engine Test Cells

Does synthetic oil reduce bearing wear? Do gasoline additives really improve combustion? These questions are investigated in a special laboratory known as an engine test cells. There are many pressure measurements needed on an engine: oil pressure, exhaust pressure, coolant pressures and any number of emission pressure measurements. Pressure transducers must be protected from the ambient environment of the test cell and still provide useful signals to a data acquisition system.

An engine test cell is a noisy, dirty and cramped room containing a running engine and everything needed to conduct the test and make the required measurements. The engine must have a sturdy mounting and a dynamometer to simulate loads. There must be piping to remove the exhaust gases and to bring in clean air. There must be adequate ventilation so that heat exchanged by the radiator can be removed from the test cell.

Pressure transducers used inside the engine test cell are mounted in a large protective enclosure that usually hangs from the wall or the ceiling. Sometimes a portable enclosure is used that has wheels so the sensors and transducers can be moved for different engine configurations.There are often several dozen transducers inside the enclosure and all of the power and signal wiring must be brought out to the data acquisition system outside the test cell. The plumbing for the transducers is a series of hoses that are connected to the outside of the enclosure and run to various points on the engine.

Engine Test Cell

Because the enclosure holding the transducers is tightly packed, the ideal transducer must be compact and easy to install. The cramped conditions in the typical test cell also require that the transducer be highly reliable; changing out a pressure transducer during a long-term engine test will inevitably create gaps in the test data. A high-level output from the transducer reduces cost for external signal conditioning for the data acquisition system.

The Validyne P55 has been successfully used in test cell environments for many years and provides the rugged stability needed for this challenging environment.  New versions of the P55 with a CAN Bus interface are now able to connect directly into the data stream from the engine’s processors.

Stand-Alone Pressure Transducer or Sensor + Electronics?

Introduction:

Validyne pressure transducers break down into two general categories:

Type 1 – A complete transducer with integral electronics

pressure transducer

 

 

 

 

 

Type 2 – A variable reluctance sensor and supporting carrier demodulator electronics.

pressure transducer

 

 

 

 

 

 

Type 1 category products include models P55, P61, P66, the P895 family and the DR800 and P532 process transmitters.

Type 2 category products include models DP15, DP360/363, DP103 with carrier demodulator models CD15, CD23/223, CD280 and CD17.

The transducers in both categories measure the same pressure ranges – so why would you choose one type over another?

Cost Effective DC Power and DC Signal:

Type 1 category transducers are generally more cost effective per point than are the sensor + electronics (Type 2) category. The Type 1 products come ready for DC power and produce a high-level DC signal, +-/5 Vdc or 4-20 mA. The Type 1 transducers include temperature compensation and are also available with higher accuracy because we can program corrections to sensor errors into the microprocessors in these products.

Type 1 products are generally ‘plug and play’ devices and are ideal for permanent installations.

Type 1 products, however, do not lend themselves to the changing of pressure ranges easily. It is possible to disassemble the sensor on a P55, for example, and replace a damaged diaphragm or install a diaphragm with a new range – but the correction factors and temperature compensation in the microprocessor will not be matched to the new assembly. Validyne can do this – and include new temperature compensation and error correction factors – but this takes time and has a cost.

Easy Range Changing:

The biggest reason to use Type 2 products is for convenient range changing. A DP15, for example, will be easier to disassemble and easier to replace a diaphragm than the Type 1 units. The sensor will be easier to calibrate with the zero and span adjustment ranges built into the external carrier demodulators. If fast frequency is important, the smaller variable reluctance sensors can be more conveniently close-coupled to piping than the larger Type 1 units and the electronics supporting Type 2 sensors have a higher low pass filter frequency available – up to 1 Khz.

Type 2 products are best suited to laboratory settings where pressure ranges are frequently changing, where a digital display is needed and where installation flexibility is important.

Type 2 products, however, do not have built-in temperature compensation, must be calibrated by the user with an appropriate pressure standard and are generally more expensive per measurement point.