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Resistance Temperature Detectors (RTD's) *

Selection Guide

Resistance Ternperature Detector IRTDI Selection Guide -

/ Step #1 - Select The Ohms Of The Element When choosing an RTD (Resistance Temperature Detector or Platinum Resistance Thermometer) for your application, you will first need to first determine the ohms of resistance for the platinum element. This is determined by the capability of your temperature indicating instruments. The Richards RTD sensor is available in 100 ohm,500 ohm, and 1000 ohm configurations. The ohm value is the base resistance of the platinum element at a reference point of 0'C. ln typical industrial applications the 100 ohm type is the most commonly used element and is the standard in this catalog. / Step #2 - Select The Alpha RTD's have a temperature coefficient or "curve" of either .003920 ohms/ohm/'C or .003850 ohms/ohm/'C. This value is commonly called the alpha of the sensor. The .003920 or "American" alpha is the U.S. industrial standard and the Japanese standard (JlS C1604-19S9). The.003850 or "European" alpha is the German (DlN 43760-1980), British (BS 1904-1984), and the lnternational Electrotechnical Commission (lEC 751-1983) standard. ln typical industrial applications the "European" curve is more commonly used than the "American" curve and is also the standard alpha in this catalog. / Step #3 - Select The Accuracy The accuracy of RTD elements are frequently classified using the DIN 43760 classification standard. This classification is also used by the lnternational Electrotechnical Commission (lEC 751). The classes are divided into four groups (A, B, C, D) by the amount of allowable resistance and temperature deviation over a temperature range. These base values are usually listed at 0"C' The small- er the deviation the lower the class (A) and the greater the accuracy of the sensor. ln order to give our customers a high quality prod- uct, all standard Richards RTD sensors perform with a accuracy greater than a class A. The standard Richards RTD has a accuracy of c0.04olo resistance or t0.1"C, which is more accurate that the DIN Class A. We also offer a very high accuracy version, which can be specified by the "AA" (American Curve) or "EE' (European Curve) in our part number. For comparison purposes, the Richards and DIN accuracy classes (at 0'C) are shown below. Richards Premium AA or EE = t0.027" resistance or t0.05"C Richards Standard A or E = =0,04o/o resistance or t0.1'C DIN Class A = +0.0670 resistance or t0,15'C DIN Class B = r0.1 2o/o rasistance or =0.3"C / Step #4 - Select The Figure Which Best Represents The Style RTD You Require Browse through our catalog and locate one of the RTD photographs which would best suite your application. Due to space limi- tations, if you do not find exactly what you are looking for, phone one of our sales engineers, and we can help with the part number. / Step #5 - Fine Tune The Part Number After locating a figure and part number, you can fine tune the sensor for your application. lf you require an American curve sen- sor and not the standard European curve, substitute the "E" with an "A" in the part number. lf you require a 500C1 and not the stan- dard 100Q sensor, substitute the "11" in the part number with a "51". 1000Cl sensors can be ordered by changing the "11" to a "101". Substitute any "X" and "Y" characters with your length requirements. RTD's are provided in four wire configurations as standard. This is the most accurate configuration. Note if you are using a transmitter you may be only able to use a three wire sensor. This can be designated by substituting the "4" in the part number with a "3". Two wire RTD's can be specified by substituting the "4" with a "2" in the part number. Note the RTD wiring configuration diagrams shown in this catalog. The standard metal sheath for RTD ele- ments is 1/4" diameter made of 316 stainless steel. lnconel sheaths can be specified by changing the "16" in the part number to a "09". Example Part Number: 4E164-11-12-24 (Four wire, European curve, 31 6ss, 1/4" Dia.,100Q, 12" probe, 24" probe and leads) Note: Richards standard RTD's have a maximum service temperature rating of 400"C (752'F). Our high temperature RTD's have a maximum service temperature rating of 650'C (1202"F). lf you would like to specify this option, add a "H" after the curve designation letter (A or E) in the catalog number. Example Part Number: 4EH164-11'12-24 (High Temp., Four wire, European curve, 316ss, 1/4" Dia.,100dt,12" probe,24" probe and leads). Page 1 38