-------------------------Monitor------------------------ The Newsletter for PC-Based Data Acquisition and Control Issue 169 www.windmill.co.uk August 2012 --------------------ISSN 1472-0221---------------------- All measurements are contaminated by noise - today we discuss how you can minimise its effects on your signals. We also pleased to announce that you can now buy the new Microlink thermocouple data logger from our web site. I hope find the newsletter useful, but should you wish to remove yourself from our mailing please go to Monitor Newsletter CONTENTS ======== * Windmill News: Thermocouple Data Logger also Measures Voltage, Flow, Level etc * How to Remove Noise from your Measurements * DAQ News Round-up ________________________________________________________ ________________________________________________________ Thermocouple Data Logger also Measures Voltage, Flow, Level, etc ________________________________________________________ The new Microlink themocouple data logger not only logs temperature data but can also measure voltage, flow, level etc. Additionally, it provides digital I/O and event and frequency counting. Read on for more details or see https://www.windmillsoft.com/daqshop/thermocouple-data-logger.html. The Thermocouple Data Logger: - Monitors 16 thermocouples or voltage signals - Has built-in linearisation for B-, E-, J-, K-, N-, R-, S- and T-type thermocouples - Automatically detects broken thermocouple leads - With extra hardware also measure strain, current and pH - Reads data over an Ethernet network or over the Internet - Reduces electrical noise with an integrating analogue-to- digital converter - Lets you select the resolution of the A-D converter from 12- to 18-bits: choose high resolution or high speed - Automatic recalibrates itself - Offers two alarms on each input - Lets you choose real-time data acquisition on your PC or stand-alone data logging Themocouple Measurement ======================= The system comprises a Microlink 851 measurement unit, an isothermal box, Windmill data acquisition and control software and technical support for life. You connect the thermocouple wires to screw terminals in the Microlink isothermal box. This keeps the temperature of the thermocouple junctions constant, measured by a cold junction sensor in the box. Plug the isothermal box into the Microlink 851 using its ribbon cable. The isothermal box will also detect broken thermocouple leads for you. For more information on monitoring thermocouples, see our tutorial on computerised themocouple measurement https://www.windmill.co.uk/temperature.html. Further Reading =============== More information on the 851-TC package: https://www.windmillsoft.com/daqshop/thermocouple-data-logger.html How to make temperature measurements - pitfalls of monitoring thermocouples and RTDs: https://www.windmill.co.uk/temperature.html ________________________________________________________ ________________________________________________________ How to Remove Noise from your Measurements Tweet ________________________________________________________ All measurements are contaminated by noise. It may be generated within the electrical components of the input amplifier: called internal noise. It may also be added to the signal as it travels down the wires to the amplifier: called external noise. Noise is more of a problem for millivolt signals, from sensors like thermocouples, than it is for larger, volt-level, signals. How do you minimise the effect of noise on your signal? Reducing Noise Generated by the Amplifier ========================================= Internal noise arises from thermal effects in the amplifier and although it can be minimised it cannot be removed completely. (The amplifier in data acquisition equipment increases the voltage signal to a level suitable for the analogue-to-digital converter.) Typically amplifiers will generate a few microvolts of internal noise which limits the resolution of the signal to this level. The amount of noise added to the signal depends on the bandwidth of the input amplifier, from the lowest frequency allowed into the amplifier to the highest. Amplifiers with a bandwidth matching that of the input signal will be less noisy than, say, feeding a 100 Hz signal into an amplifier that covers 0 to 10 MHz. Integrating A-D converters reduce noise by integrating the signal over a period, which is effectively reducing the bandwidth. Reducing Environmental Noise ============================ External noise reduction is much more of an art form. Noise is added because the signal leads act as aerials picking up environmental electrical activity. Much of this is common to both signal wires, and a differential amplifier will remove a lot of this common mode voltage. Differences between the signal wires (for example if they are separated rather than twisted together) will lead to residual voltages being added to the signal, increasing noise. Keeping the signal wires as short as possible, twisted together and as far away from electrical machinery as possible, will help. You can also shield your signal wires. Filtering Noise =============== Filtering can reduces noise errors in the signal. For most applications a low-pass filter is used. This allows through the lower frequency components but attenuates the higher frequencies. The cut-off frequency must be compatible with the frequencies present in the actual signal - as opposed to possible contamination by noise - and the sampling rate used for the A-D conversion. A low-pass filter that's used to prevent higher frequencies, in either the signal or noise, from introducing distortion into the digitised signal is known as an anti-aliasing filter. These generally have a sharper cut-off than the normal low-pass filter used to condition a signal. Anti-aliasing filters are specified according to the sampling rate of the system and there must be one filter per input signal. You can read more about filtering in Issue 8 of Monitor. Summary of Reducing Noise ========================= - Keep the signal wires short - Keep the wires away from electrical machinery - Use twisted pair wires - Use differential inputs to remove noise common the both wires - Use an integrating A-D converter to reduce mains frequency interference - Filter the signal - Consider shielding the wires Further Reading =============== Monitor Issue 8: Filtering - Removing Interference from your Signal, https://www.windmill.co.uk/filter.html Monitor Issue 122: Debugging Noisy Measuring Systems, https://www.windmill.co.uk/monitor122.html Monitor Issue 155: Differential or Single-Ended Inputs?, https://www.windmill.co.uk/monitor155.html Comments ======== ________________________________________________________ ________________________________________________________ DAQ News Round-up ________________________________________________________ Welcome to our round-up of the data acquisition and control news. If you would like to receive more timely DAQ news updates then either follow us on Twitter at http://twitter.com/#!/DataAcquisition or grab our RSS newsfeed at https://www.windmillsoft.com/monitor.xml NIST Releases Test Framework for Upgrading Smart Electrical Meters Next-generation 'smart' electrical meters for residential and commercial buildings will have computerised operating systems just as laptops or mobile devices do. Source: NIST https://www.nist.gov/ Industrial PC Market Driven by Need for Data According to the Arc Advisory Group, the Industrial PC (IPC) market continues to grow faster than most other automation hardware markets as IPC-based automation solutions replace PLCs in traditional machine control applications. Growth is also driven by the preference for IPCs in comparably new and growing areas such as wind energy. Source: Arc Advisory Group http://www.arcweb.com/ ISA Charters New Standards Committee on Intelligent Device Management The International Society of Automation has established a new standards committee, ISA108, Intelligent Device Management. The committee will define standard templates of best practices and work processes for design, development, installation and use of diagnostic and other information provided by intelligent field devices in the process industries. Source: International Society of Automation http://tinyurl.com/c6kwzhx Hairy sensors to give robots sensitive skin A coating of hairy, electronic skin could soon help robots feel the slightest breath of air. Source: New Scientist http://www.newscientist.com/ ________________________________________________________ ________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see https://www.windmill.co.uk We are happy for you to copy and distribute this newsletter, and use extracts from it on your own web site or publication, providing the above notice is included and a link back to our website is in place. An archive of previous issues is at https://www.windmill.co.uk/newsletter.html and an index of articles at https://www.windmill.co.uk/monitorindex.html Windmill Software Ltd, PO Box 58, North District Office, Manchester, M8 8QR, UK Telephone: +44 (0)161 833 2782 Facsimile: +44 (0)161 833 2190 E-mail: [email protected] https://www.windmill.co.uk/ https://www.windmillsoft.com/
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