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Controller offers simultaneous measurement and control of multiple channels

A new compact, multi-channel controller with touch-screen display is now available, which is ideal for the simultaneous measurement and control of a wide variety of process manufacturing applications.

The CMC-99 controller from Impress Sensors & Systems Ltd provides an incredible variety of input and output combinations to suit individual customer requirements. The three card slots on the reverse of the controller each comprise 16 I/O pin options, which enable the user to choose any combination of inputs and outputs to suit the application. For example, up to 48 analogue current or voltage inputs could be used; up to 16 relay/SSR outputs; 24 thermocouple inputs; or 12 RTD inputs; or a combination of these. The unit also incorporates a 24V DC digital input, enabling relays and triggers to be set up.

CMC-99 Multichannel PID Controller, Indicator & data logger

The CMC-99 is low cost compared to existing alternatives on the market and is ideal for a wide range of process applications, including centralised temperature measurement and control; multi-zone heating control; intermediate pumping station control; spraying and heating control for greenhouses; control of industrial furnaces and incinerators; and for engine test cell measurements.

Measuring just 96mm x 96mm x 100mm, the controller housing is very compact, which means the unit can be installed in restricted spaces. The controller has a 3.5-inch backlit colour TFT display and is based on the Linux operating system, with touch-screen menu navigation, offering ease of use and familiarity to the operator. A USB interface is provided on the front of the device, enabling the user to upload or download software programs quickly and easily via a USB memory stick.

PID Control
The controller is available in two power supply versions, 230V or 24V AC/DC. An auxiliary 24V DC/200mA supply output on the back of the unit enables external sensors and actuators to be connected and powered by the controller. The CMC-99 can also act as a PID process controller, providing a reliable control loop feedback mechanism for a variety of process temperature and pressure control applications.

The CMC-99 also comes with a number of communications interfaces, including two RS485 ports, two RS232, a second USB Host and an Ethernet connection, allowing the controller to integrate easily with the customer’s existing process control networks and fieldbuses.

The CMC-99’s integral software provides the user with archiving, printing and visualisation options. A variety of visual presentation display options for recorded measurements are available, including numerical display, bar graph or needle gauge display.

The CMC-99 is also available with a transparent, lockable door to IP42. An IP65 version is supplied with an additional fitted moulded frame.

For more information on the CMC-99 multi-controller, please call the sales department on 0118 981 7980 or visit the website at www.impress-sensors.co.uk

Proximity sensors are used to detect the presence of close objects and to measure distances of target bodies. They work on a laser, which means there is no physical contact with target body. The distance sensor emits an electromagnetic field or a beam of electromagnetic radiation and observes if there are any interruptions in the wave. The object is usually the target. Different targets need different types of lasers. The photoelectric sensors can work effectively for plastic targets. An inductive proximity sensor is usually used for a metal target.

The application of proximity sensors

They are used to open and close electrical circuits. As soon as there is laser contact within a certain distance from the object it opens or closes the circuit. They are commonly used in machinery and manufacturing equipment. Their other applications are also in security systems and robotics. The two basic types of proximity switches we will discuss are infrared and acoustic.

Infrared proximity switches transmit beams of infrared light. Photo-detectors record the reflections of this light. This helps to determine the distance of the object. This is a simple proximity sensor. The advanced ones can eliminate background light. Some advanced proximity sensors can directly calculate target distance without the photo-receptor.

Acoustic distance sensors use sound waves for the same purpose. A very high frequency sound wave is emitted towards the target and the time taken for it to echo is measured. Using the speed of sound the distance of the target is arrived at.

Acoustic proximity sensors are similar in principle to infrared models, but use sound instead of light. They use a transducer to transmit inaudible sound waves at various frequencies in a preset sequence and then measure the length of time the sound takes to hit a nearby object and return to a second transducer on the switch. Essentially, acoustic proximity sensors measure the time it takes for sound pulses to “echo” and use this measurement to calculate distance, just like sonar.

A temperature transmitter is a sensing device that senses and transmits the output of a sensed temperature. In a process control system, process control transmitters are used to measure the process parameters and variables. Temperature transmitters are widely used for controlling industrial processes. They can sense a temperature and transmits the output to a remote location.

A process temperature transmitter offers an output that is related to the actual temperature of the sensed surface. The output obtained from the temperature transmitter can either be communicated to a VDU or to another device so that the process can be controlled and monitored.

How does a temperature transmitter work?

A temperature transmitter introduces a current into the temperature sensor and the resulting voltage drop across the sensor is used for measuring the resistance. This voltage is then converted into a digital form with the help of an analogue to digital converter and offered to a microprocessor.

Once the digital output is fed to the microprocessor, it converts the calculated voltage into a digital value of the temperature. The temperature transmitter comprises a housing and a temperature probe that is attached to the housing. For monitoring a process temperature, the transmitter often includes a sensor, such as a thermocouple or a resistance temperature device (RTD).

An RTD changes the resistance with the change in temperature. This temperature can be measured by calculating the resistance of an RTD. Similarly, a thermocouple also offers a voltage output with a change in temperature.

On stand 29 at this year’s WWEM (Water, Wastewater & Environmental Monitoring) exhibition (10-11 November 2010) at the Telford International Centre in Shropshire, sensor and instrumentation specialist Impress Sensors & Systems Ltd will be showcasing a range of new products, including submersible hydrostatic level transmitters and a multi-channel process controller.

The main focus of stand 29 will be Impress’ comprehensive range of submersible hydrostatic level transmitters. The SDI-12L for example, offers an SDI-12 digital output with an inbuilt high accuracy temperature sensor, which can be used in depths of up to 200 metres. This unit uses either a stainless steel silicon-based pressure sensor or a ceramic pressure sensor in marine-bronze. Both versions use piezoresistive technology, ensuring long-term stability and repeatability of measurements.

The SDI-12L is suitable for monitoring river and reservoir levels; tanks and vessels in process plants; seawater and estuary levels; borehole water levels; Tsunami and tidal monitoring systems; wave height measurement; environmental monitoring; and V-notch weir flow measurement.

The stainless steel version offers a higher resolution of pressure measurement to around 12-13 Bit and has a much lower signal-to-noise ratio, providing a very smooth and accurate method of level measurement.

The ceramic pressure sensor version is better suited to marine use, where standard devices may suffer from corrosion. These units are ideal for seawater, estuary and saline applications. Due to its SDI-12 compatibility, the transmitter can be corrected according to the specific density of the media being measured and local gravity can be set within the device, adding further to the accuracy of the unit.

The SDI-12L is just part of Impress’ comprehensive family of submersible hydrostatic level transmitters, which also includes ATEX-approved and SIL-rated level transmitters for hazardous areas; submersibles for aggressive media in PVDF, PVC and PEEK materials and for chemical dosing, SIP and CIP process. Other submersible transmitters are available with flush diaphragms for viscous or pasty media. Extremely high over-pressure units are also available, which protect transmitters in tank or pipe blockage situations.

Multi-channel controller

As well as submersible transmitters, Impress’ stand will also feature a full working demonstration of the company’s new compact, multi-channel, touch-screen controller, the CMC-99. This unit is ideal for the simultaneous measurement and control of a variety of water and wastewater applications, including intermediate pumping station measurement and control.

The CMC-99 controller provides an incredible variety of input and output combinations to suit individual customer requirements. The three card slots on the reverse of the controller each comprise 16 I/O pin options, which enable the user to choose any combination of inputs and outputs to suit the application. For example, up to 48 analogue current or voltage inputs could be used; up to 16 relay/SSR outputs; 24 thermocouple inputs; or 12 RTD inputs; or a combination of these. The unit also incorporates a 24V DC digital input, enabling relays and triggers to be set up.

For more information on Impress Sensors’ range of products, or for a sensor demonstration, please call in on stand 29 at WWEM 2010 or call the sales department on 0118 981 7980. Alternatively, visit the website at www.impress-sensors.co.uk

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Note to Editors:

About Impress Sensors & Systems Ltd

Impress Sensors & Systems Ltd (www.impress-sensors.co.uk) is a rapidly expanding UK manufacturer and distributor of instrumentation products based in Aldermaston, Berkshire. The company prides itself on its expertise in pressure measurement and its knowledge of general instrumentation. The company manufactures its own range of standard and custom-designed pressure instruments in the UK, and distributes a wide portfolio of instrumentation products from its European partners – BD Sensors in Germany and Metallux in Switzerland. Impress specialises in offering a customised service in applications where standard products may not satisfy the technical requirements and price aspirations of customers. The company boasts the necessary technical expertise in mechanical, electronic and application engineering that enables it to supply instruments tailored to the customer’s requirements.

Eddy current and capacitive distance sensors utilise a reference coil to produce a magnetic field in a target and observe the field close to an adjacent sending coil to find out the distance from the target. As the target starts getting nearer to the sensor, the magnetic field is disrupted. This disruption is sensed by the second coil.

Eddy current and capacitive distance sensors also measure the changes in field due to the existence of nearby conductive objects. Field detection and field generation information is offered in ranges from kHz to MHz. As eddy current distance sensor operates by interrupting a magnetic field. It is also possible to have non-magnetic or magnetic targets, using either nonferrous or ferrous materials.

The specifications of eddy current and capacitive distance sensors

One of the most important specifications of eddy current distance sensors is the range they are capable of measuring. Sensing frequency is the other important specification. The sensing frequency is actually a frequency range on which the sensor device operates.

Static resolution is also an important specification of the eddy current and capacitive distance sensor. Resolution is actually the smallest rise of quantity that can be determined. It informs you about how much change in quantity is required for the sensor to sense the change.

For considerably small changes in position, you will need a sensor with a smaller resolution. Lastly, temperature compensation is another important specification to consider when purchasing eddy current and capacitive distance sensors. Temperature compensation is the ability to maintain output stability during changing or fluctuating ambient temperature conditions.

Ultrasonic sensors are generally used for an extensive range of non-contact proximity, presence or distance measurement applications. These devices transmit a small burst of ultrasonic sound towards the object, which then reflects the sound back to the sensing device.

The system measures the time taken by the echo to return to the sensing device and calculates the distance to the object using the speed of sound in a given medium. With the wide range of distance sensors available in the market, all differ from each other in their electronic features, mounting configurations and environmental sealing.

Acoustically, distance sensors operate at different frequencies. They even have different radiation patterns. Selecting the best distance sensor to suit the mechanical and environmental requirements for a particular application is not that difficult. Evaluating electronic features of different distance sensor models can help you choose the best distance sensor to suit your needs.

What you should know about ultrasonic distance sensors

Many users are not aware of the fact that acoustic subtleties can create major effects on the operation of an ultrasonic distance sensor and the measurements that are being made with them. While purchasing an ultrasonic distance sensor, you should look for the one with best acoustic properties using a beam or frequency pattern.

Some factors that affect distance measurement

Variations in the following can affect the distance measurement of an ultrasonic temperature sensor.

• speed of sound
• attenuation
• wavelength
• amplitude of return echo
• amplitude of background noise
• sound radiation pattern

Getting a better understanding about the variations in acoustical parameters of both the target and the environment can greatly help you get the right ultrasonic distance sensor to suit your needs.

As an essential part of most industrial operations, temperature measurement is usually accomplished with the help of temperature sensors. This is a resistance or thermocouple temperature that is either immersed in a liquid or that comes into contact with a hard surface. Temperature sensors are known to have overlapping temperature ranges; however, all of them have certain advantages depending on their application.

When selecting temperature sensors, there are many considerations that have to be made according to the application of the device. Here are two types of temperature sensors that are used for most operations.

RTDs – Resistance Temperature Detectors (RTDs) are a type of temperature sensor that is made from copper, platinum and nickel. The basis of this operation relies on the increase of resistivity which takes place when the temperature of the material increases. Generally, RTDs have a simple construction which compromises of connecting a sensing element to a non-conducting element that is made from mica, glass or ceramic. The element is capable of measuring the resistance and a temperature result is obtained from this result.

Thermocouples – These differ from RTDs in terms of structure as they consist of two metals, joined at one end. This can pick up a voltage which can be converted to a temperature reading. The physical range of these temperature sensors is quite large as extension wire can be connected to the sensing junction (the meeting point of both metals). Thermocouples are more affordable than RTDs; however they may produce imprecise results if there are other components in the electric circuit.

In addition to these, infrared temperature sensors are also being used for temperature measurement these days. Understanding which type of temperature sensor suits you best can help operations go smoothly.