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December 23rd, 2010
Pressure sensors are used in a wide range of industries to protect the machinery from being overworked. These devices monitor the pressure in your machinery and ensure that the operator is alerted as soon as the pressure goes above the danger mark.
For the highest possible accuracy, it is advisable to opt for a pressure sensor that is not easily corruptible and has a high resolution.
Digital output pressure sensors
These pressure sensors do not suffer from signal losses or interference like the standard analogue ones. It is known to transmit either a complete signal or none at all, thereby reducing the chances of an inconsistent reading.
Achieving an output signal
In order to achieve a powerful output signal, a digital converter of at least 16 bit resolution is required. This converter ensures that the pressure sensor achieves better precision levels at 0.01% full scale.
No digital – analogue conversion
With digital output pressure sensors, you do not need to convert the digital signal to analogue at any stage between the pressure sensor and the display. This is because the signal obtained can be easily interfaced to a data acquisition card with the help of a digital connection.
Zero linearity errors
Another added benefit of using a digital output pressure sensor is that it uses a microprocessor inside the digital pressure sensor. This microprocessor can be used to characterise the pressure sensor over many other pressure and temperature points. This feature helps in eliminating all linearity errors.
Hysteresis and repeatability of the sensor
The accuracy of most standard pressure sensors is bound to be affected due to the hysteresis and repeatability of the sensor technology used. However, a digital output pressure sensor has the potential to provide the most accurate signal when used in conjunction with the stable sensing technology. The RS485 is the most commonly used interface for general applications.
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December 22nd, 2010
Pressure sensors are devices that are used to monitor the load on the heavy duty machinery in factories. With the help of pressure sensors, the operator can be given up-to-date information on the machinery. These machines can be shut down if the load on them increases.
Pressure sensors play an important role in preventing damage to the expensive equipment used in the factories. From time to time, maintenance can also be carried out. With the advancement of time, pressure sensors have undergone a major change. With the introduction of wireless pressure sensors, companies find it easy to keep a track on the performance of their machinery. Given below are some of the uses of pressure sensors.
Common reasons to use wireless pressure sensors
Factories have started using wireless pressure sensors to avoid the clutter of wires. Tyre pressure, transducer miniaturisation, multi point sensing and enhanced signal to noise ratio are some of the other common reasons to use wireless pressure sensors.
Keller pressure sensors
Keller pressure sensors use the piezo resistance law to function. According to this law, the pressure applied on the device is directly proportional to the resistance. Various industries use the Keller pressure sensor for their machinery and equipment.
Other industrial uses of wireless pressure sensors
Wireless pressure sensors are very common in many industries. The petroleum industry, waste water facilities and manufacturing giants rely heavily on the wireless pressure system.
An important advantage of the wireless pressure sensor is that they can be used to study the liquid chemicals and beverages. Wireless pressure systems have become an integral part of every major business.
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December 22nd, 2010
Level switches are sensor devices that are specifically used for detecting the powder or liquid levels. These level measurements are mostly indicated with the help of an electrical switching action. Level switches are mostly point level switches that measure whether the level of container has gone over or reached the predetermined point.
The multiple point switches can be incorporated together to offer a stepped version of the constant level. These level switches can either be used as alarm devices or as control switches for turning something off or on like a pump. They can also be used for sending signals to valve actuators.
One of the special characteristics of level switches is that their output can either be solid state or electro-mechanical, either normally closed or normally open. The typical options for throws and poles are also available. Most level switches have a one or two throws or poles. However, some manufacturers do offer customised level switches for special applications.
Technologies used for measuring level include:
• Air bubbler technology
• RF or capacitive admittance
• Electrical resistivity or conductivity
• Magnetic or mechanical floats
• Differential pressure
• Radio frequency
Some important specifications of level switches
The measuring range is an important specification to consider while looking for level switches. At the same time, it is also necessary to consider the ratings for voltage and current.
Level switches can be mounted in different ways, depending on the specific needs of your application. They are mostly mounted on the bottom, top or on the side of the container that holds the substance to be measured.
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December 21st, 2010
The RTD temperature transmitters are used for converting the RTD resistance measurement into current signals. This eliminates problems in RTD signal transmissions that are naturally caused due to lead resistance. Errors in RTD circuits (particularly 2 and 3 wire RTDs) are mostly due to the added leadwire resistance between the instrument and the sensor.
If you are looking for RTD temperature transmitters, the sensor connections, environment, user interfaces, transmitter input, features and specifications are some important parameters you should consider. The reference resistance, reference materials, sensed temperature and other inputs are some transmitter input specifications you must consider when choosing RTD temperature transmitters.
Options for reference materials include nickel alloys or nickel, copper and platinum. For the measurement integrity of RTDs, platinum is the most commonly used metal. While nickel alloys and nickel are affordable and commonly used metals, they are not as precise as platinum. On the other hand, copper is rarely used as RTD element. This is mainly because the low resistivity of the element is quite longer compared to the platinum element.
Other considerations while looking for RTD temperature transmitters
The temperature range that is to be sensed and transmitted is an important consideration. Input, output and mounting of RTD temperature transmitters are other specifications you need to consider. Common mounting styles include thermowell or thermohead mounting, cabinet or board mounting and DIN rail mounting.
Inputs include analogue current, analogue voltage and resistance input. Similarly, common outputs include analogue voltage, switch or relay output and analogue current. User interface options include digital front panel, computer interface and analogue front panel.
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December 21st, 2010
The capacitive linear position sensors are specially designed to take the non-contact measurement of vibration, position, displacement and thickness or run-out measurements. These types of sensors can be used on non-conductive and conductive target materials. However, they can be quite sensitive to environmental parameters that alter the dielectric constant of medium between the target (air) and the sensor.
The measuring range of capacitive linear position sensors is one of the most important specifications to look for when getting one. Maximum usable range of these sensors is another important specification of the capacitive distance sensors. This is the complete range over which the device can offer sensible readings, even if it is non linear.
Accuracy and outputs of capacitive distance sensors
The accuracy of capacitive distance sensors is usually measured as a percentage of its full-scale measurement. Considering the sensing frequency range is also equally important. When it comes to output, a number of different options are available.
Analogue outputs of capacitive distance sensors include frequency or voltage. On the other hand, digital outputs include parallel, serial or other outputs like TTL output. Another alternative for the output can be a change in the state of switches or an alarm.
The packaging of capacitive distance sensors is an important consideration. Sometimes, the sensor element with signal conditioning or no external packaging is available. A transducer is a more common and complex device that comes with signal conditioning or/and packaging. It offers outputs like 4-20mA, DC volts, etc.
Meters and instruments are also available. They are mostly self-contained units that offer output near the device and also include signal conditioning or processing.
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December 20th, 2010
Pressure transducers are available in many different types. These types can be used to measure many different types of pressure variables including differential and vacuum pressure. They can also measure things such as the partial pressure of gases.
Operation
Pressure transducers measure pressure levels such as water pressure in storage tanks and convert this pressure into a proportional output signal. This output signal can then be transmitted to a remote location to be used in a process control application. In the past pressure transducers made use of bellows and a wound flattened tubing. The older models also incorporated variable resistors and slidewires. However, changing times has brought about a gradual change in the design of the pressure transducers. The modern pressure transducers are designed with high-accuracy strain gauge and solid-state sensing techniques.
Why were pressure transducers developed?
Pressure transducers were developed for many purposes. These devices enabled operators to control and monitor remote pressure variables. The devices can also eliminate any sort of potentially hazardous situations where pressure levels rise too high.
These superior features of pressure transducers have contributed to their use in many industrial applications.
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December 20th, 2010
Pressure transducers and transmitters are widely used in manufacturing plants. However, several users fail to understand the difference between these two devices.
Pressure transducers
The definition of a pressure transducer has undergone a tremendous change over the years. A pressure transducer can now be described as a device that is employed to convert pressure into an electrical signal. Pressure transducers are available in many different types. Some of the different types of pressure transducers are mentioned below.
• Thick film transducers
• Thin film transducers
• Semi conductor strain gauge transducers
All the above mentioned transducers are used to provide an electrical signal. Usually, these transducers provide a millivolt output signal which changes with any variation in pressure.
Pressure transmitters
A pressure transmitter is basically a pressure transducer with additional electronics to provide a 4 to 20 mA output signal. A 4 to 20mA current loop output is the standard unit for the transmission of pressure transducer signals.
In the past pressure transmitters were only used in huge processing plants. The sensors back then were heavy and rather expensive. However, several manufacturing plants now employ the 4-20mA output signal pressure transmitters in their process control applications. Their compact size now means they are used widely. However, the compact size has added to the confusion between a pressure transmitter and a transducer.
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December 19th, 2010
Pressure sensors are nowadays commonly used in many manufacturing plants. As the name suggests, pressure sensors check the pressure levels of gases or liquids.
Pressure sensors as transducers
Pressure sensors perform as a transducer. A transducer in simple terms can be described as a device that is used to convert one form of energy into another. The pressure sensor produces an electric signal when pressure is imposed on the device.
Application of pressure sensors
These sensors are widely used for controlling and monitoring applications commonly used in manufacturing plants. These sensors also prove useful while measuring other variables. Some of the variables for which pressure sensors are used are mentioned below.
• Fluid
• Gas flow
• Speed
• Water level
Pressure sensors are also known by other terms such as pressure transducers, pressure transmitters and pressure indicators. These devices differ on the basis of the application and technology used in their production. They may also vary on the basis of the overall cost of the product. More than 50 technologies are currently employed to produce pressure sensors.
Pressure sensors can be used to determine the altitude of a plane or other airborne object. In this application they function on the basis that the air pressure changes relative to the altitude.
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December 18th, 2010
Do you require high pressure levels for production or operational purposes? If your answer is yes, then you must think about buying the latest pressure gauging devices. Pressure sensors are manufactured or designed in such a manner that they can easily monitor the pressure generated or imposed on their specific application. These sensors are also known as pressure transducers and transmitters.
With these advanced sensors, you can measure the pressure of different variables such as fluid, speed, altitude and gas flow.
Which types are available today?
To satisfy different industrial needs, manufacturers have introduced various kinds of pressure sensors. The four most popular sensors are vacuum pressure sensors, absolute pressure sensors, gauge pressure sensors, differential pressure sensors. Today, you will find that differential pressure sensors are installed in many industrial devices because they can monitor the pressure levels between two setpoint values.
Pressure sensors – What technologies are used?
Today, mechanical deflection and fibre optics are commonly used in the design and manufacture of pressure sensors. Pressure sensors which use mechanical deflection use mechanical properties to check pressure levels.
Besides the above mentioned technologies, vibrating elements, micro-electromechanical systems and semiconductor piezoresistive technologies are also used.
Where are pressure sensors used?
As pressure is imposed in many applications, various types of pressure sensors are used in different fields. These include medical instrumentation, weather applications and aerospace. You will also find pressure sensors in things we use every day such as car alarms.
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December 17th, 2010
Linear position sensors utilise non-contact and contact methods to measure the speed and/or position of an object. They also use different sensing technologies for accurate measurement.
While capacitance sensors are used with both non-conductive and conductive materials, they are quite sensitive to environmental variables.
Eddy current sensors comprise of two coils – an active coil for indicating the presence of a conducting target and a secondary coil for completing the bridge circuit.
Fibre optic sensors utilise a pair of adjoining fibres to carry the light to a target and returned light from the object.
Inductive sensors are non-contact devices used for determining the co-ordinates of an object from a reference point.
Linear encoders digitise and sense the position changes of a device for control systems.
On the other hand, linear potentiometers produce a resistance output that is proportional to the position or displacement of the object.
LVDTs or linear variable differential transformers produce electrical outputs that are proportional to the position of a cylindrical, solid core.
Other types of distance sensors
In the case of magneto-resistive sensors, the resistance of the conducting strip works as a function of magnitude and direction of the applied magnetic field. With these sensors, the displacement infers with the change of magnetic field that is generated from a ferromagnetic material.
While photo-electrical sensors use reflected light to measure displacement or distance, ultrasonic sensors reflect the acoustic signals to determine the distance depending on the measurement medium’s propagation velocity and the signal’s return time. Before purchasing distance sensors, it is always recommended to thoroughly understand your application needs.
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