- Product Categories
- Friendly Links
The bit about the accuracy of thermocouple measurements
2014-02-25 Reads : 56
A thermocouple is used to measure the temperature of the mining industry required product, its high cost and wide measurement range has been widely used. Boilers, cement plants, power plants, chemical plants, steel mills, and so manufacturers of instrumentation necessary supplies. Can be measured directly from the surface of various production range of 0 ℃ to 1300 ℃ steam and liquid, gas and solid temperatures. According to state regulations, in accordance with IEC international standard indexing number of platinum and rhodium 30 - 6 platinum and rhodium, platinum and rhodium - platinum, nickel and chromium - nickel silicon, nickel, chromium - constantan thermocouple assembly, etc., as a temperature sensor usually display instruments, recording instruments and supporting the use of electronic regulator. Thermocouple signal conditioning should be designed to avoid ground loops grounding thermocouple measurements, but also a path to the amplifier's input bias current measurement, an insulated thermocouple. Furthermore, if the first thermocouple is grounded, the input range of the amplifier should be designed to handle any differences in ground potential between the thermocouple and the measurement system ground. Grounding options, using different types of tips. Non-isolated systems, dual power signal conditioning system is usually more powerful foundation and type of exposure. Because of its wide common mode input range, dual power amplifier can handle large voltage difference between the printed circuit board (PCB) ground and thermocouple head on the ground. Single-supply systems can work satisfactorily in all three cases below ground single supply configuration if the amplifier common mode range has some ability to measure. Common-mode processing is limited to certain single-supply system, a bias voltage is useful yardstick thermocouple. The project is well insulated thermocouple tips, or if the overall measurement system is isolated. However, this is not recommended for non-isolated systems for measuring ground or exposed thermocouples. Practical solutions for thermocouple: thermocouple signal conditioning is more complex than other temperature measurement system. The time required to design and debug signal conditioning can improve time to market. The error signal conditioning, especially in the reference junction compensation section, can lead to low precision. The following solutions to resolve these problems. The first detailed simulation of a simple integrated hardware solutions, combined with direct thermocouple reference junction compensation using a single integrated circuit. Details of the program two reference junction temperature compensation package software provides a more accurate thermocouple measurements and flexible use of various types of thermocouples. Measurement Solution: Optimize simple shows the measured K-type thermocouple. It is based on the use of ad8495 thermocouple amplifier, which is designed to measure the K-type thermocouple. This simulation solutions are designed to optimize the minimum time: it has a simple signal chain and unwanted software coding. Measurement Solution 1: Optimize simple. How to address this simple signal chain K-type thermocouple signal conditioning requirements? Gain and output scaling factor: small thermocouple signal amplification ad8495 gain of 122, resulting in 5-mv / ° output signal sensitivity (200 ° /). Noise Reduction: high frequency common mode and differential mode noise is generated by an external radio frequency interference filters. Low frequency common mode noise is rejected ad8495 instrumentation amplifier. Any remaining noise is generated by the external post filter. Reference junction compensation: ad8495, which includes a temperature sensor to compensate for changes in ambient temperature must be maintained in the vicinity of the reference connection reference terminal accurate temperature compensation at the same temperature. Non-linear calibration correction ad8495: to 5 mV / ° K-type thermocouple wire output of the linear part of the linearity error of less than 2 ° C at 25 - ° ℃ to +400 ℃ temperature range °. If the temperature is outside this range needs, Analog Devices application note an-1087 describes how to find a table or equation can be used in a microprocessor extended temperature range. Powerful thermocouple temperature measurement over a wide temperature range, but they are often not the first choice, temperature measurements, and design time because the tradeoff between the required accuracy. This paper presents a cost-effective way to solve these problems. The first solution to reduce the complexity of measuring a reference junction compensation means hardware-based simulation. It results in a simple signal chain requires no software programming, relying on the integration provides ad8495 thermocouple amplifier to produce a 5-mv / ° output signal, you can enter a variety of microcontroller analog input. Option II provides the highest accuracy measurements, you can also use a variety of thermocouple types. Software-based reference junction compensation technology, which relies on high-precision digital temperature sensor adt7320 provide a more accurate measure than the reference junction compensation is implemented, until now. The adt7320 is fully calibrated and specified -40 ° ℃ to + 125 ℃ temperature range °. Completely transparent, unlike conventional thermistors or resistance sensor, it does not need the expensive calibration step, the plate assembly, or a linear calibration factor which does not consume any processor or memory resources of the routine. Only micro-power consumption, it avoids the problem of self-heating undermine the accuracy of traditional resistive sensor solutions.
keywords: Thermocouple,
Admin>>>
You are the 10689 visitor
Copyright © GuangDong ICP No. 10089450, The Huai'an Dwyer Instrument Co., Ltd. All rights reserved.
Technical support: ShenZhen AllWays Technology Development Co., Ltd.
AllSources Network's Disclaimer: The legitimacy of the enterprise information does not undertake any guarantee responsibility
You are the 10689 visitor
Copyright © GuangDong ICP No. 10089450, The Huai'an Dwyer Instrument Co., Ltd. All rights reserved.
Technical support: ShenZhen AllWays Technology Development Co., Ltd.
AllSources Network's Disclaimer: The legitimacy of the enterprise information does not undertake any guarantee responsibility