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Displacement, Load And Pressure Sensors


About us
RDP is a designer and manufacturer and distributor of LVDT displacement transducers, amplifiers, load cells and pressure sensors for use in a wide range of applications. We are privately owned by the two directors who started the company in 1966. Our extensive range LVDT displacement sensors and amplifiers are manufactured by us at our UK head office and factory. RDP was one of the first manufacturers of LVDT displacement transducers and the first to build the LVDT signal conditioning amplifier into the sensor.
What is a transducer?
A transducer (which is also commonly known as a sensor) is a device which converts a physical parameter into an electrical signal. There are many different types of sensor which measure many different physical parameters but our range concentrates on displacement or position, load and pressure.
What is a displacement transducer?
A displacement transducer is a device which converts a length, movement or position into an electrical or digital signal. There are many different types but because of the fact that there is no physical contact in the sensing element ours are one of the most reliable types available.
What is an LVDT Displacement sensor?
LVDT stands for Linear Variable Differential Transformer. The moving part of the LVDT is connected to a core rod. Inside the body of the LVDT there is a primary coil (in the centre) and two secondary coils (at either end); the position of the core varies the induction into the two secondary coils. External or internal electronics then converts this signal into a dc output proportional to position of the core. Because the core does not touch the coils there is no contact so the output has infinite resolution.
Where are LVDT Displacement Transducers used?
LVDT displacement transducers are used in many different applications. The most common are in industrial production where the need to know the position of a cutting tool for example is essential for the control system. Our displacement transducers have visited the depths of the oceans for valve position measurement and been into space to measure the deflection in a mirror. They're also equally at home in your factory or laboratory!
How reliable are LVDT sensors?
LVDT displacement sensors are very reliable. The basic LVDT construction is very robust as it comprises precision wound coils which are encased in stainless steel. Because the measurement principle uses a magnetic field there is no contact between the moving core (the part that makes the LVDT transducer output change) and the body of the LVDT so in the case of an unguided sensor there is absolutely no contact and therefore zero friction. Because of this our displacement transducers have been used in applications where they have been in service at the bottom of the sea for decades.
In which environments can LVDT displacement sensors be used?
That depends on the type! Our standard industrial series displacement sensors are designed for factories, laboratories and research departments. They might be measuring the elongation of a test sample as it is loaded or the position of a steam valve in a power station. Because of the way LVDT sensors work we can weld the electronics inside and allow the fluid to enter the tube inside the LVDT. This means that they can be used under water; deep under water. Some of our sea water submersible sensors can go down to 2.2km in sea water. By controlling the materials used both inside and outside the transducer we can also design sensors for high (600℃) and low (-220℃) temperature as well as very high nuclear radiation. We have been manufacturing LVDT displacement sensors for over 50 years and in that time we have developed a very wide range of standard products as well as very many specials.
What is a Micropulse Displacement Sensor?
A micropulse sensor is a different type of displacement / position sensor particularly suited for longer measurement applications of the order of 0.5 to 7m. They are primarily designed for fitting inside a hydraulic piston but can be used in many applications. Like an LVDT their principle is non-contact. The micropulse transducer comprises an electronics head at one end of a steel tube, the length of the tube varies with the measurement range. The measurement is made of the position of a magnet, the field of which passes through the steel tube. The electronics head launches a current pulse down a conductor inside the tube, when this interacts with the magnetic field an acoustic pulse is generated which travels back to the electronics head. The position of the magnet with respect to the lead changes the time between the launch of the current pulse and the arrival of the acoustic pulse. This difference is processed into a very accurate measurement of the position of the magnet with respect to the electronics head.
What is a load cell?
A load cell or force sensor is a device that converts force or load into an electrical signal; a set of digital bathroom scales probably use at least one load cell. There are many different types of load sensors but ours are strain gauge type load cells. The load cell itself is a mechanical structure designed such that one part of it deforms in a linear manner proportional to the load or force applied. This part of the load cell is strain gauged. A strain gauge is a resistive device that changes in resistance when it is stretched; this is what converts the physical parameter (the mechanical extension of the load cell) into an electrical signal.
What are load cells used for?
Load cells are used in any application where you need to measure load or force. Anything from weighing a lorry (on a weighbridge) to measuring the force required to insert one component into another. Load cells (or force sensors) are very often used in conjunction with LVDT displacement transduccers so that the properties of a test sample can be measured (so how far it extends for a given force).
What are pressure sensors?
Pressure sensors are devices that converts the pressure of a fluid or gas into an electrical signal. The air-line you use to fill your car tyres at the fuel station or the blood pressure monitor used by your doctor both contain pressure sensors. They are many different types of pressure sensors but ours work by using a strain gauge to measure the deflection of a diaphragm as the pressure changes.
What is a pressure transducer used for?
Pressure transducers of our type are most commonly used for measuring the pressure of hydraulic fluid in hydraulic pistons. Additionally they are commonly used for proof testing of pressure vessels.
What is an amplifier?
In the context of our products an amplifier is an electronic device that boosts the very small signals from a transducer into a bigger signal that can be used by machine control systems or data logging devices. Our range of amplifiers includes units that work with LVDTs and (because they need a different approach) different amplifiers that work with strain gauge transducers such as load cells and pressure transducers. The amplifiers often need to be located near to the transducer so some of them are housed in water resistant housings. Some of our amplifiers have digital displays so that the transducer value can be directly displayed as a number.