4-20mA CURRENT TRANSMITTER with Sensor Excitation and Linearization

Transcription

1 -ma CURRNT TRANSMITTR with Sensor xcitation and Linearization FATURS LOW UNADJUSTD RROR TWO PRCISION CURRNT SOURCS µa ACH RTD OR BRIDG XCITATION LINARIZATION TWO OR THR-WIR RTD OPRATION LOW OFFST DRIFT:.µV/ C LOW OUTPUT CURRNT NOIS: nap-p HIGH PSR: db min HIGH CMR: db min WID SUPPLY RANG:.V TO V -PIN DIP AND SO- SOIC PACKAGS DSCRIPTION The is a monolithic -ma, two-wire current transmitter with two precision current sources. It provides complete current excitation for Platinum RTD temperature sensors and bridges, instrumentation amplifier, and current output circuitry on a single integrated circuit. Versatile linearization circuitry provides a nd-order correction to the RTD, typically achieving a : improvement in linearity. Instrumentation amplifier gain can be configured for a wide range of temperature or pressure measurements. Total unadjusted error of the complete current transmitter is low enough to permit use without adjustment in many applications. This includes zero output current drift, span drift and nonlinearity. The operates on loop power supply voltages down to.v. The is available in -pin plastic DIP and SO- surface-mount packages and is specified for the C to + C industrial temperature range. APPLICATIONS INDUSTRIAL PROCSS CONTROL FACTORY AUTOMATION SCADA RMOT DATA ACQUISITION RMOT TMPRATUR AND PRSSUR TRANSDUCRS Nonlinearity (%) RTD C I R =.ma I R =.ma Pt NONLINARITY CORRCTION USING Process Temperature ( C) + V LIN VRG Uncorrected RTD Nonlinearity Corrected Nonlinearity - ma + C.V to V V PS V O R L International Airport Industrial Park Mailing Address: PO Box, Tucson, AZ Street Address: S. Tucson Blvd., Tucson, AZ Tel: () - Twx: -- Internet: FAXLine: () - (US/Canada Only) Cable: BBRCORP Telex: - FAX: () - Immediate Product Info: () - Burr-Brown Corporation PDS-B Printed in U.S.A. February, SBOS

2 SPCIFICATIONS At T A = + C, V+ = V, and TIPC external transistor, unless otherwise noted. P, U PA, UA PARAMTR CONDITIONS MIN TYP MAX MIN TYP MAX UNITS OUTPUT Output Current quation = (/ ) + ma, in Volts, in Ω A Output Current, Specified Range ma Over-Scale Limit ma Under-Scale Limit I RG = V... ma ZRO OUTPUT () = V, = ma Initial rror ± ± ± µa vs Temperature ±. ±. ±. µa/ C vs Supply Voltage, V+ V+ =.V to V.. µa/v vs Common-Mode Voltage V CM =.V to.v (). µa/v vs V RG Output Current. µa/ma Noise:.Hz to Hz. µap-p SPAN Span quation (Transconductance) S = / A/V Initial rror () Full Scale ( ) = mv ±. ±. ±. % vs Temperature () ± ± ppm/ C Nonlinearity: Ideal Input () Full Scale ( ) = mv.. % INPUT () Offset Voltage V CM = V ± ± ± µv vs Temperature ±. ±. ± µv/ C vs Supply Voltage, V+ V+ =.V to V ±. ± µv/v vs Common-Mode Voltage, V CM =.V to.v () ± ± ± µv/v RTI (CMRR) Common-Mode Input Range ().. V Input Bias Current na vs Temperature pa/ C Input Offset Current ±. ± ± na vs Temperature pa/ C Impedance: Differential. GΩ pf Common-Mode GΩ pf Noise:.Hz to Hz. µvp-p CURRNT SOURCS V O = V () Current µa Accuracy ±. ±. ±. % vs Temperature ± ± ± ppm/ C vs Power Supply, V+ V+ =.V to V ± ± ppm/v Matching ±. ±. ±. % vs Temperature ± ± ± ppm/ C vs Power Supply, V+ V+ =.V to V ppm/v Compliance Voltage, Positive (V+) (V+). V Negative (). V Output Impedance MΩ Noise:.Hz to Hz. µap-p V () RG. V Accuracy ±. ±. V vs Temperature ±. mv/ C vs Supply Voltage, V+ mv/v Output Current ± ma Output Impedance Ω LINARIZATION R LIN (internal) kω Accuracy ±. ±. ± % vs Temperature ± ± ppm/ C POWR SUPPLY Specified + V Voltage Range +. + V TMPRATUR RANG Specification, T MIN to T MAX + C Operating + C Storage + C Thermal Resistance, θ JA -Pin DIP C/W SO- Surface-Mount C/W Specification same as P, U. NOTS: () Describes accuracy of the ma low-scale offset current. Does not include input amplifier effects. Can be trimmed to zero. () Voltage measured with respect to pin. () Does not include initial error or TCR of gain-setting resistor,. () Increasing the full-scale input range improves nonlinearity. () Does not include Zero Output initial error. () Current source output voltage with respect to pin.

3 PIN CONFIGURATION Top View I R NC I R + V LIN V RG V+ B (Base) (mitter) NC = No Internal Connection. PACKAG/ORDRING INFORMATION DIP and SOIC PACKAG DRAWING TMPRATUR PRODUCT PACKAG NUMBR () RANG PA -Pin Plastic DIP C to + C P -Pin Plastic DIP C to + C UA SO- Surface Mount C to + C U SO- Surface Mount C to + C ABSOLUT MAXIMUM RATINGS () Power Supply, V+ (referenced to pin)... V + Input Voltage,, (referenced to pin)... V to V+ Storage Temperature Range... C to + C Lead Temperature (soldering, s)... + C Output Current Limit... Continuous Junction Temperature... + C NOT: () Stresses above these ratings may cause permanent damage. LCTROSTATIC DISCHARG SNSITIVITY This integrated circuit can be damaged by SD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. SD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. NOT: () For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. FUNCTIONAL BLOCK DIAGRAM V LIN I R I R µa µa V RG V+ +.V R LIN kω µa B Q V I = µa + IN Ω Ω = ma + ( ) The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems.

4 TYPICAL PRFORMANC CURVS At T A = + C, V+ = V, unless otherwise noted. Transconductance ( Log ma/v) TRANSCONDUCTANC vs FRQUNCY = Ω = Ω = kω ma/div ma ma = kω STP RSPONS = Ω k k k Frequency (Hz) M µs/div Common-Mode Rejection (db) COMMON-MOD RJCTION vs FRQUNCY Full-Scale Input = mv = Ω = kω k k k Frequency (Hz) M Power Supply Rejection (db) POWR-SUPPLY RJCTION vs FRQUNCY = Ω = kω k k k Frequency (Hz) M Over-Scale Current (ma) OVR-SCAL CURRNT vs TMPRATUR With xternal Transistor V+ = V V+ =.V V+ = V Under-Scale Current (ma)..... UNDR-SCAL CURRNT vs TMPRATUR V+ =.V to V Temperature ( C). Temperature ( C)

5 TYPICAL PRFORMANC CURVS (CONT) At T A = + C, V+ = V, unless otherwise noted. k INPUT VOLTAG AND CURRNT NOIS DNSITY vs FRQUNCY k k ZRO OUTPUT AND RFRNC CURRNT NOIS vs FRQUNCY Input Voltage Noise (nv/ Hz) k Current Noise k Input Current Noise (fa/ Hz) Noise (pa/ Hz) k Zero Output Current Reference Current Voltage Noise k k Frequency (Hz) k k k Frequency (Hz) k Input Bias and Offset Current (na) INPUT BIAS AND OFFST CURRNT vs TMPRATUR Temperature ( C) S +I B I B Zero Output Current rror (µa) ZRO OUTPUT CURRNT RROR vs TMPRATUR Temperature ( C) Percent of Units (%). INPUT OFFST VOLTAG DRIFT PRODUCTION DISTRIBUTION Typical Production Distribution of Packaged Units..%.% Input Offset Voltage Drift (µv/ C) Percent of Units (%) ZRO OUTPUT DRIFT PRODUCTION DISTRIBUTION Typical Production Distribution of Packaged Units Zero Output Drift (µa/ C)

6 TYPICAL PRFORMANC CURVS (CONT) At T A = + C, V+ = V, unless otherwise noted. Percent of Units (%) CURRNT SOURC DRIFT PRODUCTION DISTRIBUTION Typical Production Distribution of Packaged Units. I R AND I R Included..%.% Percent of Units (%) CURRNT SOURC MATCHING DRIFT PRODUCTION DISTRIBUTION Typical Production Distribution of Packaged Units..%.% Current Source Drift (ppm/ C) Current Source Matching Drift (ppm/ C). V RG OUTPUT VOLTAG vs V RG OUTPUT CURRNT +. RFRNC CURRNT RROR vs TMPRATUR V RG Output Voltage (V) C C C NOT: Above ma, Zero Output Degrades Reference Current rror (%) V RG Output Current (ma). Temperature ( C)

7 APPLICATION INFORMATION Figure shows the basic connection diagram for the. The loop power supply, V PS, provides power for all circuitry. Output loop current is measured as a voltage across the series load resistor, R L. Two matched.ma current sources drive the RTD and zero-setting resistor, R Z. The instrumentation amplifier input of the measures the voltage difference between the RTD and R Z. The value of R Z is chosen to be equal to the resistance of the RTD at the low-scale (minimum) measurement temperature. R Z can be adjusted to achieve ma output at the minimum measurement temperature to correct for input offset voltage and reference current mismatch of the. R CM provides an additional voltage drop to bias the inputs of the within their common-mode input range. R CM should be bypassed with a.µf capacitor to minimize common-mode noise. Resistor sets the gain of the instrumentation amplifier according to the desired temperature range. R LIN provides second-order linearization correction to the RTD, typically achieving a : improvement in linearity. An additional resistor is required for three-wire RTD connections, see Figure. The transfer function through the complete instrumentation amplifier and voltage-to-current converter is: = ma + (/ ) ( in volts, in ohms) where is the differential input voltage. As evident from the transfer function, if no is used the gain is zero and the output is simply the s zero current. The value of varies slightly for two-wire RTD and three-wire RTD connections with linearization. can be calculated from the equations given in Figure (two-wire RTD connection) and Table I (three-wire RTD connection). The pin is the return path for all current from the current sources and V RG. The pin allows any current used in external circuitry to be sensed by the and to be included in the output current without causing an error. The V RG pin provides an on-chip voltage source of approximately.v and is suitable for powering external input circuitry (refer to Figure ). It is a moderately accurate voltage reference it is not the same reference used to set the µa current references. V RG is capable of sourcing approximately ma of current. xceeding ma may affect the ma zero output. I R =.ma I R =.ma V LIN I + R I R V RG V+.V to V Possible choices for Q (see text). TYP N TIPC TIPC PACKAG TO- TO- TO- R LIN () () B Q.µF - ma V O R L + V PS RTD () R Z R CM = kω.µf I = ma + ( O ) NOTS: () R Z = RTD resistance at minimum measured temperature. R = (R +R Z ) (R R Z ) () R R R R LIN = LIN (R R ) () (R R R Z ) where R = RTD Resistance at (T MIN + T MAX )/ R = RTD Resistance at T MAX R LIN = kω (Internal) FIGUR. Basic Two-Wire RTD Temperature Measurement Circuit with Linearization.

8 A negative input voltage,, will cause the output current to be less than ma. Increasingly negative will cause the output current to limit at approximately.ma. Refer to the typical curve Under-Scale Current vs Temperature. Increasingly positive input voltage (greater than the fullscale input) will produce increasing output current according to the transfer function, up to the output current limit of approximately ma. Refer to the typical curve Over- Scale Current vs Temperature. XTRNAL TRANSISTOR Transistor Q conducts the majority of the signal-dependent -ma loop current. Using an external transistor isolates the majority of the power dissipation from the precision input and reference circuitry of the, maintaining excellent accuracy. Since the external transistor is inside a feedback loop its characteristics are not critical. Requirements are: V CO = V min, β = min and P D = mw. Power dissipation requirements may be lower if the loop power supply voltage is less than V. Some possible choices for Q are listed in Figure. The can be operated without this external transistor, however, accuracy will be somewhat degraded due to the internal power dissipation. Operation without Q is not recommended for extended temperature ranges. A resistor (R =.kω) connected between the pin and the (emitter) pin may be needed for operation below C without Q to guarantee the full ma full-scale output, especially with V+ near.v. V+ R Q =.kω.µf FIGUR. Operation Without xternal Transistor. For operation without external transistor, connect a.kω resistor between pin and pin. See text for discussion of performance. LOOP POWR SUPPLY The voltage applied to the, V+, is measured with respect to the connection, pin. V+ can range from.v to V. The loop supply voltage, V PS, will differ from the voltage applied to the according to the voltage drop on the current sensing resistor, R L (plus any other voltage drop in the line). If a low loop supply voltage is used, R L (including the loop wiring resistance) must be made a relatively low value to assure that V+ remains.v or greater for the maximum loop current of ma: R L max = (V+).V ma R WIRING It is recommended to design for V+ equal or greater than.v with loop currents up to ma to allow for out-ofrange input conditions. The low operating voltage (.V) of the allows operation directly from personal computer power supplies (V ±%). When used with the RCV Current Loop Receiver (Figure ), load resistor voltage drop is limited to V. ADJUSTING INITIAL RRORS Many applications require adjustment of initial errors. Input offset and reference current mismatch errors can be corrected by adjustment of the zero resistor, R Z. Adjusting the gain-setting resistor,, corrects any errors associated with gain. TWO-WIR AND THR-WIR RTD CONNCTIONS In Figure, the RTD can be located remotely simply by extending the two connections to the RTD. With this remote two-wire connection to the RTD, line resistance will introduce error. This error can be partially corrected by adjusting the values of R Z,, and R LIN. A better method for remotely located RTDs is the three-wire RTD connection shown in Figure. This circuit offers improved accuracy. R Z s current is routed through a third wire to the RTD. Assuming line resistance is equal in RTD lines and, this produces a small common-mode voltage which is rejected by the. A second resistor, R LIN, is required for linearization. Note that although the two-wire and three-wire RTD connection circuits are very similar, the gain-setting resistor,, has slightly different equations: Two-wire: Three-wire: = R (R + R Z )(R R Z ) R R = (R R Z )(R R Z ) R R where R Z = RTD resistance at T MIN R = RTD resistance at (T MIN + T MAX )/ R = RTD resistance at T MAX

9 MASURMNT TMPRATUR SPAN T ( C) T MIN C C C C C C C C C C C./../././././././.././ C./.././././././././ C /. / / / / / / / C / / / / / / / C /. / / / / / C /. / / / / C /. / / / C /. / / C /. / C /. C /. = (R R Z )(R R Z ) (R R ) R LIN = R LIN (R R ) (R R R Z ) R LIN = (R LIN + )(R R ) (R R R Z ) R Z / R LIN R LIN NOT: The values listed in the table are % resistors (in Ω). xact values may be calculated from the following equations: R Z = RTD resistance at minimum measured temperature. where R = RTD resistance at (T MIN + T MAX )/ R = RTD resistance at T MAX R LIN = kω (Internal) XAMPL: The measurement range is C to + C for a -wire Pt RTD connection. Determine the values for R S,, R LIN, and R LIN. Look up the values from the chart or calculate the values according to the equations provided. MTHOD : TABL LOOK UP For T MIN = C and T = C, the % values are: R Z =.Ω R LIN =.kω = Ω R LIN = kω MTHOD : CALCULATION Step : Determine R Z, R, and R. R Z is the RTD resistance at the minimum measured temperature,t MIN = C. Using equation () at right gives R Z =.Ω (% value is.ω). R is the RTD resistance at the maximum measured temperature, T MAX = C. Using equation () at right gives R =.Ω. R is the RTD resistance at the midpoint measured temperature, T MID = (T MIN + T MAX )/ = C. R is NOT the average of R Z and R. Using equation () at right gives R =.Ω. Step : Calculate, R LIN, and R LIN using equations above. =.Ω (% value is Ω) R LIN =.kω (% value is.kω) R LIN =.kω (% value is kω) Calculation of Pt Resistance Values (according to DIN IC ) quation () Temperature range from C to C: R (T) = [ +. T. T. (T ) T ] quation () Temperature range from C to + C: R (T) = ( +. T. T ) where: R (T) is the resistance in Ω at temperature T. T is the temperature in C. NOT: Most RTD manufacturers provide reference tables for resistance values at various temperatures. TABL I. R Z,, R LIN, and R LIN Standard % Resistor Values for Three-Wire Pt RTD Connection with Linearization. To maintain good accuracy, at least % (or better) resistors should be used for. Table I provides standard % resistor values for a three-wire Pt RTD connection with linearization. LINARIZATION RTD temperature sensors are inherently (but predictably) nonlinear. With the addition of one or two external resistors, R LIN and R LIN, it is possible to compensate for most of this nonlinearity resulting in : improvement in linearity over the uncompensated output.

10 A typical two-wire RTD application with linearization is shown in Figure. Resistor R LIN provides positive feedback and controls linearity correction. R LIN is chosen according to the desired temperature range. An equation is given in Figure. In three-wire RTD connections, an additional resistor, R LIN, is required. As with the two-wire RTD application, R LIN provides positive feedback for linearization. R LIN provides an offset canceling current to compensate for wiring resistance encountered in remotely located RTDs. R LIN and R LIN are chosen such that their currents are equal. This makes the voltage drop in the wiring resistance to the RTD a commonmode signal which is rejected by the. The nearest standard % resistor values for R LIN and R LIN should be adequate for most applications. Table I provides the % resistor values for a three-wire Pt RTD connection. If no linearity correction is desired, the V LIN pin should be left open. With no linearization, = V FS, where V FS = full-scale input range. RTDs The text and figures thus far have assumed a Pt RTD. With higher resistance RTDs, the temperature range and input voltage variation should be evaluated to ensure proper common-mode biasing of the inputs. As mentioned earlier, R CM can be adjusted to provide an additional voltage drop to bias the inputs of the within their common-mode input range. RROR ANALYSIS Table II shows how to calculate the effect various error sources have on circuit accuracy. A sample error calculation for a typical RTD measurement circuit (Pt RTD, C measurement span) is provided. The results reveal the s excellent accuracy, in this case.% unadjusted. Adjusting resistors and R Z for gain and offset errors improves circuit accuracy to.%. Note that these are worst case errors; guaranteed maximum values were used in the calculations and all errors were assumed to be positive (additive). The achieves performance which is difficult to obtain with discrete circuitry and requires less space. OPN-CIRCUIT PROTCTION The optional transistor Q in Figure provides predictable behavior with open-circuit RTD connections. It assures that if any one of the three RTD connections is broken, the s output current will go to either its high current limit ( ma) or low current limit (.ma). This is easily detected as an out-of-range condition. R LIN () R LIN () + V LIN I R I R V RG V+ () B Q.µF QUAL line resistances here creates a small common-mode voltage which is rejected by. R Z () R CM = Ω.µF (R LIN ) (R LIN ) RTD Q () N NOTS: () See Table I for resistor equations and % values. () Q optional. Provides predictable output current if any one RTD connection is broken: Resistance in this line causes a small common-mode voltage which is rejected by. (R LIN ) OPN RTD TRMINAL.mA ma.ma FIGUR. Three-Wire Connection for Remotely Located RTDs.

11 SAMPL RROR CALCULATION RTD value at ma Output (R RTD MIN ) Ω RTD Measurement Range C Ambient Temperature Range ( T A ) C Supply Voltage Change ( V+) V Common-Mode Voltage Change ( CM).V RROR SAMPL (ppm of Full Scale) RROR SOURC RROR QUATION RROR CALCULATION () UNADJ. ADJUST. INPUT Input Offset Voltage V OS /( MAX ) µv/(µa.ω/ C C) vs Common-Mode CMRR CM/( MAX ) µv/v.v/(µa.ω/ C C) Input Bias Current I B /I RF.µA/µA Input Offset Current S R RTD MIN /( MAX ) na Ω/(µA.Ω/ C C) Total Input rror: XCITATION Current Reference Accuracy I RF Accuracy (%)/%.%/% vs Supply (I RF vs V+) V+ ppm/v V Current Reference Matching I RF Matching (%)/% µa.%/% µa Ω/(µA.Ω/ C C) R RTD MIN /( MAX ) vs Supply (I RF matching vs V+) V+ ppm/v V µa Ω/(µA.Ω/ C C) R RTD MIN /( MAX ) Total xcitation rror: GAIN Span Span rror (%)/%.%/% Nonlinearity Nonlinearity (%)/%.%/% Total Gain rror: OUTPUT Zero Output (I ZRO - ma) /µa µa/µa vs Supply (I ZRO vs V+) V+/µA.µA/V V/µA Total Output rror: DRIFT ( T A = C) Input Offset Voltage Drift T A /( MAX ).µv/ C C/(µA.Ω/ C C) Input Bias Current (typical) Drift T A /µa pa/ C C/µA.. Input Offset Current (typical) Drift T A R RTD MIN /( MAX ) pa/ C C W/(µA.Ω/ C C).. Current Reference Accuracy Drift T A ppm/ C C Current Reference Matching Drift T A µa R RTD MIN /( MAX ) ppm/ C C µa Ω/(µA.Ω/ C C) Span Drift T A ppm/ C C Zero Output Drift T A /µa.µa/ C C/µA Total Drift rror: NOIS (. to Hz, typ) Input Offset Voltage v n /( MAX ).µv/(µa.ω/ C C) Current Reference I RF Noise R RTD MIN /( MAX ) na Ω/(µA.Ω/ C C) Zero Output I ZRO Noise/µA.µA/µA Total Noise rror: TOTAL RROR: (.%) (.%) NOT (): All errors are min/max and referred to input unless otherwise stated. TABL II. rror Calculation.

12 RVRS-VOLTAG PROTCTION The s low compliance rating (.V) permits the use of various voltage protection methods without compromising operating range. Figure shows a diode bridge circuit which allows normal operation even when the voltage connection lines are reversed. The bridge causes a two diode drop (approximately.v) loss in loop supply voltage. This results in a compliance voltage of approximately V satisfactory for most applications. If.V drop in loop supply is too much, a diode can be inserted in series with the loop supply voltage and the V+ pin. This protects against reverse output connection lines with only a.v loss in loop supply voltage. SURG PROTCTION Remote connections to current transmitters can sometimes be subjected to voltage surges. It is prudent to limit the maximum surge voltage applied to the to as low as practical. Various zener diode and surge clamping diodes are specially designed for this purpose. Select a clamp diode with as low a voltage rating as possible for best protection. For example, a V protection diode will assure proper transmitter operation at normal loop voltages, yet will provide an appropriate level of protection against voltage surges. Characterization tests on three production lots showed no damage to the within loop supply voltages up to V. Most surge protection zener diodes have a diode characteristic in the forward direction that will conduct excessive current, possibly damaging receiving-side circuitry if the loop connections are reversed. If a surge protection diode is used, a series diode or diode bridge should be used for protection against reversed connections. RADIO FRQUNCY INTRFRNC The long wire lengths of current loops invite radio frequency interference. RF can be rectified by the sensitive input circuitry of the causing errors. This generally appears as an unstable output current that varies with the position of loop supply or input wiring. If the RTD sensor is remotely located, the interference may enter at the input terminals. For integrated transmitter assemblies with short connection to the sensor, the interference more likely comes from the current loop connections. Bypass capacitors on the input reduce or eliminate this input interference. Connect these bypass capacitors to the terminal as shown in Figure. Although the dc voltage at the terminal is not equal to V (at the loop supply, V PS ) this circuit point can be considered the transmitter s ground. The.µF capacitor connected between V+ and may help minimize output interference. V+ NOT: () Zener Diode V: NA or General Semiconductor Transorb TM NA. Use lower voltage zener diodes with loop power supply voltages less than V for increased protection. See Over-Voltage Surge Protection. B.µF D () N Diodes The diode bridge causes a.v loss in loop supply voltage. R L V PS Maximum V PS must be less than minimum voltage rating of zener diode. FIGUR. Reverse Voltage Operation and Over-Voltage Surge Protection.

13 kω V LIN I + R I R V RG V+ R LIN R LIN B.µF kω R Z.µF.µF RTD () R CM.µF NOT: () Bypass capacitors can be connected to either the pin or the pin. FIGUR. Input Bypassing Technique with Linearization. I RG < ma V Type J V+ / LTC V LIN + I R I R V RG V+ R F kω R Ω R F kω Ω B Ω kω / LTC V + = ma + ( ) Ω R CM = Ω R (G = + F = ) R FIGUR. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold Junction Compensation.

14 V LIN I + R I R V RG V+ N +V µf Pt C to C RTD R LIN Ω R Z Ω Ω B Q.µF = ma ma RCV µf V O = to V V R CM = kω.µf NOT: A two-wire RTD connection is shown. For remotely located RTDs, a three-wire RTD conection is recommended. becomes Ω, R LIN is Ω. See Figure and Table I. FIGUR. ±V Powered Transmitter/Receiver Loop. RTD R LIN R Z R LIN V LIN I + R I R V RG V+ B Q = ma ma N.µF NOT: A three-wire RTD connection is shown. For a two-wire RTD connection eliminate R LIN. RCV µf µf ISO +V Isolated Power from PWS V V+ V O V V R CM = kω.µf FIGUR. Isolated Transmitter/Receiver Loop.

15 .ma V LIN I + R I R V RG V+ B R CM = kω () NOT: () Use R CM to adjust the common-mode voltage to within.v to.v. FIGUR. Bridge Input, Current xcitation.

16 IMPORTANT NOTIC Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. Customers are responsible for their applications using TI components. In order to minimize risks associated with the customer s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI s publication of information regarding any third party s products or services does not constitute TI s approval, warranty or endorsement thereof. Copyright, Texas Instruments Incorporated