Instrument Signal Conditioners

Extracting HART Data from Smart Instruments - According to the FieldComm Group (formerly the HART Communications Foundation), there are more than 30 million HART-enabled instruments installed in chemical and process plants worldwide, and most process transmitters made today are HART compatible. The HART digital signal often contains valuable process measurements and other variables including instrument status, diagnostic data, alarms, calibration values and alert messages. However, many systems fail to utilize the critical information available from HART-enabled transmitters, valve positioners, flowmeters and other "smart" devices. This article from Moore Industries shows how a HART interface device can serve as a simple and cost-effective solution for gathering HART information.

Signal Conditioning Engineers Guide - This guide contains a wealth of information on basic principles, applications, and functional safety. At over 23 Meg this is a massive download, but it is worth it - from Pepperl+Fuchs.

The following technical papers are from Acromag:

Temperature Measurement Using RTDs - A RTD or Resistance Temperature Detector is a passive circuit element whose resistance increases with increasing temperature in a predictable manner. In choosing one you must consider a RTDs temperature coefficient of resistance (TCR), its relative sensitivity, its accuracy and repeatability, interchangeability, stability and drift characteristics, its insulation resistance, its response time, plus its packaging and the thermal transfer mechanism between the sensed material and the sensor element. You must also consider the negative effects of corrosion and contamination, shock and vibration, self-heating, meter loading, and in some cases, even thermoelectric effects.

Temperature Measurement Using Thermocouples - You are probably somewhat familiar with the thermocouple, but you must understand that choosing the type (J, K, T, etc.) is not as simple as just picking a compatible temperature span. You must give consideration to the sensor materials, the ambient temperature range, the sensor's sensitivity, and its reaction with the measurement environment. You must also be aware of the inherent limitations of the thermocouple and potential error sources. This white paper will help you to make an informed selection between sensor types and avoid potential problems in your application.

The following Signal Conditioner papers are from

Introduction to Signal Conditioners - A signal conditioner is a device that converts one type of electronic signal into a another type of signal. Its primary use is to convert a signal that may be difficult to read by conventional instrumentation into a more easily read format. In performing this conversion a number of functions may take place.

Analogue I/O Functionality - Today, digital computers and other microprocessor-based devices have replaced analog recording and display technologies in all but the simplest data acquisition applications. And while computers have had an undeniably positive impact on the practice of data acquisition, they speak only a binary language of ones and zeroes. Manufacturing processes and natural phenomena, however, are still by their very nature analog. That is, natural processes tend to vary smoothly over time, not discontinuously changing states from black to white, from on to off. To be meaningfully recorded or manipulated by a computer then, analog measurements such as pressure, temperature, flow rate, and position must be translated into digital representations.

Digital I/O Functionality - In contrast to analog transducers that sense continuous variables such as pressure and temperature, many transducers provide an output that is one of two states: high or low, open or closed. A pressure might be too high or a temperature too low, triggering closure of a switch. Outputs, too, are not strictly analog-solenoid valves typically are opened or closed, many pumps and heaters are simply turned on or off. Pulse signals are another form of digital I/O, with one rotation of a turbine flowmeter or tachometer corresponding to a single, countable event. Digital I/O also can be used for parallel communications among plug-in expansion cards, and to generate clock and other timing signals.

Analogue Signal Transmission - Although the microprocessor and digital network technologies have fundamentally reinvented the ways in which today's data acquisition systems handle data, much laboratory and manufacturing information is still communicated the "old" way, via analog electrical signals. And a fundamental understanding of how analog signal transmission works must first begin with a discussion of electrical basics. To understand the ways in which an analog signal is transmitted over a circuit, it is first important to understand the relationships that make analog signal transmission possible. It is the fundamental relationship between voltage, current, and electrical resistance (Figure 3-1) that allow either a continuously varying current or voltage to represent a continuous process variable.

Digital Signal Transmission - Industrial networks that transmit data using digital signals often are an integral part of a data acquisition or process control solution. A basic understanding of the network technologies that are available for various applications is required to make the best implementation decisions-decisions that can have a profound effect on the ability to adapt to ever-changing technologies.

Data Acquisition Hardware - Previous chapters of this volume have acquainted you with the technology of how input/output (I/O) signals are generated, conditioned, linearized, and transmitted to a host computer or controlling system. In this chapter, we will look at the different kinds of data acquisition hardware that are available to help you perform all of these functions.

Acronyms at a Glance - A useful list.

Signal Conditioning - This article reviews signal conditioning equipment features such as accuracy, adjustability, isolation, surge withstand capability, RFI/EMI protection, packaging, and repairability. Where possible, it also examines the relative importance of various features - from Acromag.

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