® XTR103 XTR 103 XTR 103 4-20mA Current Transmitter with RTD EXCITATION AND LINEARIZATION FEATURES APPLICATIONS ● LESS THAN ±1% TOTAL ADJUSTED ERROR, –40°C TO +85°C ● RTD EXCITATION AND LINEARIZATION ● INDUSTRIAL PROCESS CONTROL ● FACTORY AUTOMATION ● SCADA ● TWO OR THREE-WIRE RTD OPERATION ● WIDE SUPPLY RANGE: 9V to 40V ● HIGH PSR: 110dB min ● HIGH CMR: 80dB min Pt100 NONLINEARITY CORRECTION USING XTR103 5 DESCRIPTION The XTR103 is a monolithic 4-20mA, two-wire current transmitter designed for Platinum RTD temperature sensors. It provides complete RTD current excitation, instrumentation amplifier, linearization, and current output circuitry on a single integrated circuit. Nonlinearity (%) 4 Versatile linearization circuitry provides a 2nd-order correction to the RTD, typically achieving a 40:1 improvement in linearity. 3 Uncorrected RTD Nonlinearity 2 Corrected Nonlinearity 1 0 –1 –200°C Instrumentation amplifier gain can be configured for a wide range of temperature measurements. Total adjusted error of the complete current transmitter, including the linearized RTD is less than ±1% over the full –40 to +85°C operating temperature range. This includes zero drift, span drift and nonlinearity. The XTR103 operates on loop power supply voltages down to 9V. +850°C Process Temperature (°C) IR = 0.8mA IR = 0.8mA 9 to 40V + The XTR103 is available in 16-pin plastic DIP and SOL-16 surface-mount packages specified for the –40°C to +85°C temperature range. VPS 4-20 mA VO XTR103 RG RL RTD – RLIN International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111 Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 © 1992 Burr-Brown Corporation PDS-1145E Printed in U.S.A. October, 1993 SPECIFICATIONS ELECTRICAL At TA = +25°C, V+ = 24V, and 2N6121 external transistor, unless otherwise noted. XTR103BP/BU PARAMETER CONDITIONS OUTPUT Output Current Equation Total Adjusted Error (1) Output Current, Specified Range Over-Scale Limit Under Scale-Limit Full Scale Output Error Noise: 0.1Hz to 1kHz ZERO OUTPUT(2) Initial Error vs Temperature vs Supply Voltage, V+ vs Common-Mode Voltage SPAN Span Equation (Transconductance) Untrimmed Error vs Temperature(4) Nonlinearity: Ideal Input RTD Input INPUT Differential Range Input Voltage Range(3) Common-Mode Rejection Impedance: Differential Common-Mode Offset Voltage vs Temperature vs Supply Voltage, V+ Input Bias Current vs Temperature Input Offset Current vs Temperature CURRENT SOURCES(5) Current Accuracy vs Temperature vs Power Supply, V+ Compliance Voltage(3) Matching vs Temperature vs Power Supply, V+ MIN VIN = 1V, RG = ∞ RG = 40Ω VIN = 0, RG = ∞ 4 ±5 ±0.2 0.5 0.1 V+ = 9V to 40V(3) VCM = 2V to 4V(3) Pt100: –200°C to +850°C RLIN = 1127Ω RG = ∞ 2 80 4V(3) V+ = 9V to 40V(3) MIN TYP ✻ ✻ ✻ ✻ ✻ ±50 ±0.5 2 2 ✻ ✻ ✻ S = 0.016 + 40/RG ±0.1 ±1 ±20 ±50 0.01 0.1 RG ≥ 75Ω VIN = 2V to XTR103AP/AU MAX MAX IO = VIN • (0.016 + 40/RG) + 4mA, VIN in Volts, RG in Ω ±1 ±2 4 20 ✻ ✻ 34 40 ✻ ✻ 3.6 3.8 ✻ ✻ ±15 ±50 ✻ ±100 8 ✻ TMIN to TMAX 110 1 4 100 3 0.5 ±0.5 ±1 130 100 0.1 2 0.01 0.8 ±0.25 ±25 50 V+ = 9V to 40V(3) ✻ ✻ ±2.5 ±2.5 ✻ 250 2 20 0.25 ✻ ✻ ±50 ✻ ±0.5 ±50 A % of FS mA mA mA µA µAp-p ±100 ±1 ✻ ✻ mA µA µA/°C µA/V µA/V ✻ ±100 ✻ ✻ A/V % ppm/°C % % ✻ ✻ ✻ ✻ ✻ ✻ ±2 ✻ ✻ ✻ ✻ ✻ UNITS ✻ ±5 ✻ ✻ ✻ ✻ ±1 ±100 mA % ppm/°C ppm/V V % ppm/°C ppm/V ✻ 9 40 ✻ ✻ V –40 –40 85 125 ✻ ✻ ✻ ✻ °C °C °C/W ±10 10 V+ = 9V to 40V(3) 80 ✻ ✻ ✻ ✻ ✻ ±50 V V dB GΩ GΩ mV µV/°C dB nA nA/°C nA nA/°C (V+) – 5 ±0.5 ±25 (V–IN) – 0.2 POWER SUPPLY Voltage Range(3), V+ TEMPERATURE RANGE Specification, TMIN to TMAX Operating θJA TYP ✻ Specification same as XTR103BP. NOTES: (1) Includes corrected Pt100 nonlinearity for process measurement spans greater than 100°C, and over-temperature zero and span effects. Does not include initial offset and gain errors which are normally trimmed to zero at 25°C. (2) Describes accuracy of the 4mA low-scale offset current. Does not include input amplifier effects. Can be trimmed to zero. (3) Voltage measured with respect to IO pin. (4) Does not include TCR of gain-setting resistor, RG. (5) Measured with RLIN = ∞ to disable linearization feature. ® XTR103 2 PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS Power Supply, V+ (referenced to IO pin) .......................................... 40V Input Voltage, V+IN , V–IN (referenced to IO pin) ........................ 0V to V+ Storage Temperature Range ........................................ –55°C to +125°C Lead Temperature (soldering, 10s) .............................................. +300°C Output Current Limit ............................................................... Continuous Junction Temperature ................................................................... +165°C TOP VIEW Zero Adjust 1 16 Zero Adjust Zero Adjust 2 15 B (Base) – VIN 3 14 EINT (Internal Emitter) + VIN 4 13 IR2 RG 5 12 IR1 RG 6 11 E (Emitter) IO 7 10 V+ RLIN 8 9 ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. RLIN ESD 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. PACKAGE/ORDERING INFORMATION PRODUCT PACKAGE PACKAGE DRAWING NUMBER(1) XTR103AP XTR103BP XTR103AU XTR103BU 16-pin Plastic DIP 16-pin Plastic DIP SOL-16 Surface Mount SOL-16 Surface Mount 180 180 211 211 TEMPERATURE RANGE –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. 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. ® 3 XTR103 TYPICAL PERFORMANCE CURVES At TA = +25°C, V+ = 24VDC, unless otherwise noted. TRANSCONDUCTANCE vs FREQUENCY STEP RESPONSE 60 RS = ∞ RG = 25Ω 20mA RG = 100Ω 40 RG = 400Ω RS = 25Ω RG = 2kΩ RG = ∞ 20 5mA/Div Transconductance (20 Log mA/V) 80 4mA 0 100 1k 10k 100k 100µs/Div 1M Frequency (Hz) POWER SUPPLY REJECTION vs FREQUENCY (RTI) COMMON-MODE REJECTION vs FREQUENCY (RTI) 120 140 100 Power Supply Rejection (dB) G = 0.16A/V (RG = 400Ω) CMR (dB) 80 60 40 20 G = 0.16A/V (RG = 400Ω) 120 100 80 60 40 20 0 0 0.1 1 10 100 1k 10k 0.1 100k 1 10 LOOP RESISTANCE vs LOOP POWER SUPPLY 1750 1k 10k 100k INPUT OFFSET VOLTAGE vs LOOP POWER SUPPLY 60 1550Ω 1500 Span = ∆IO = 16mA 50 RL max = 1250 Without external transistor (V+) – 9V 20mA ∆VOS (µV) Loop Resistance, RL (Ω ) 100 Frequency (Hz) Frequency (Hz) 1000 750 Operating Region 500 00Ω 40 RL =1 00Ω 30 RL kΩ 20 RL With external transistor 250 =1 10 9V 0 10 20 30 40 50 10 20 30 Loop Power Supply Voltage, VPS (V) Loop Power Supply Voltage, VPS (V) ® XTR103 RL = 1kΩ RL = 600Ω RL = 100Ω 0 0 =6 4 40 TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, +V = 24VDC, unless otherwise noted. INPUT CURRENT NOISE DENSITY vs FREQUENCY OUTPUT CURRENT NOISE DENSITY vs FREQUENCY 10 Input Current Noise (pA/ Hz ) RG = ∞ 1 1 0.1 0.1 0.1 1 10 100 1k 10k 0.1 100k 1 10 100 1k 10k 100k Frequency (Hz) Frequency (Hz) INPUT VOLTAGE NOISE DENSITY vs FREQUENCY 1k Noise Voltage (nV/ Hz ) Output Current Noise (pA/ Hz) 10 100 10 0.1 1 10 100 1k 10k 100k Frequency (Hz) ® 5 XTR103 APPLICATION INFORMATION Negative input voltage, VIN, will cause the output current to be less than 4mA. Increasingly negative VIN will cause the output current to limit at approximately 3.6mA. Figure 1 shows the basic connection diagram for the XTR103. The loop power supply, VPS provides power for all circuitry. Output loop current is measured as a voltage across the series load resistor, RL. Increasingly positive input voltage (greater than VFS) will produce increasing output current according to the transfer function, up to the output current limit of approximately 34mA. Two matched 0.8mA current sources drive the RTD and zero-setting resistor, RZ. The instrumentation amplifier input of the XTR103 measures the voltage difference between the RTD and RZ. The value of RZ is chosen to be equal to the resistance of the RTD at the low-scale (minimum) measurement temperature. RZ can be adjusted to achieve 4mA output at the minimum measurement temperature to correct for input offset voltage and reference current mismatch of the XTR103. EXTERNAL TRANSISTOR Transistor Q1 conducts the majority of the signal-dependent 4-20mA loop current. Using an external transistor isolates the majority of the power dissipation from the precision input and reference circuitry of the XTR103, maintaining excellent accuracy. Since the external transistor is inside a feedback loop its characteristics are not critical. Requirements are: VCEO = 45V min, β = 40 min and PD = 800mW. Power dissipation requirements may be lower if the loop power supply voltage is less than 40V. Some possible choices for Q1 are listed in Figure 1. RCM provides an additional voltage drop to bias the inputs of the XTR103 within their common-mode range. Resistor, RG, sets the gain of the instrumentation amplifier according to the desired temperature measurement range. The transfer function through the complete instrumentation amplifier and voltage-to-current converter is: The XTR103 can be operated without this external transistor by connecting pin 11 to 14 (see Figure 2). Accuracy will be somewhat degraded by the additional internal power dissipation. This effect is most pronounced when the input stage is set for high gain (for low full-scale input voltage). The typical performance curve “Input Offset Voltage vs Loop Supply Voltage” describes this behavior. IO = VIN • (0.016 + 40/RG) + 4mA, (VIN in volts, RG in ohms, RLIN = ∞) where VIN is the differential input voltage. With no RG connected (RG = ∞), a 0V to 1V input produces a 4-20mA output current. With RG = 25Ω, a 0V to 10mV input produces a 4-20mA output current. Other values for RG can be calculated according to the desired full-scale input voltage, VFS, with the formula in Figure 1. VIN = V+IN – V–IN = IR (RTD – RZ) Possible choices for Q1 (see text). 13 4 5 IR = 0.8mA IR = 0.8mA + IR V+IN IR 10 V+ 4-20 mA B XTR103 E RG RLIN – 3 V IN RLIN 9 8 RLIN (3) (1, 3) RTD 15 Q1 0.01µF 11 IO + + RL – VPS – 7 IO = 4mA + VIN (0.016 + 40 ) RG RZ NOTES: (1) RZ = RTD resistance at the minimum measured temperature. R CM = 1.5kΩ (2) RG = 0.01µF 2500 Ω 1 –1 VFS , where VFS is Full Scale VIN. (3) See Table I for values. FIGURE 1. Basic RTD Temperature Measurement Circuit. ® XTR103 TO-225 TO-220 TO-220 RG RG 6 PACKAGE 12 (2, 3) VIN – TYPE 2N4922 TIP29B TIP31B 6 The low operating voltage (9V) of the XTR103 allows operation directly from personal computer power supplies (12V ±5%). When used with the RCV420 Current Loop Receiver (Figure 8), load resistor voltage drop is limited to 1.5V. 10 V+ LINEARIZATION 11 E XTR103 On-chip linearization circuitry creates a signal-dependent variation in the two matching current sources. Both current sources are varied equally according to the following equation: 500 • VIN IR1 = IR2 = 0.8 + RLIN 0.01µF EINT 14 IO 7 (IR in mA, VIN in volts, RLIN in ohms) (maximum IR = 1.0mA) For operation without external transistor, connect pin 11 to pin 14. See text for discussion of performance. This varying excitation provides a 2nd-order term to the transfer function (including the RTD) which can correct the RTD’s nonlinearity. The correction is controlled by resistor RLIN which is chosen according to the desired temperature measurement range. Table I provides the RG, RZ and RLIN resistor values for a Pt100 RTD. FIGURE 2. Operation Without External Transistor. LOOP POWER SUPPLY The voltage applied to the XTR103, V+, is measured with respect to the IO connection, pin 7. V+ can range from 9V to 40V. The loop supply voltage, VPS, will differ from the voltage applied to the XTR103 according to the voltage drop on the current sensing resistor, RL (plus any other voltage drop in the line). If no linearity correction is desired, do not connect a resistor to the RLIN pins (RLIN = ∞). This will cause the excitation current sources to remain a constant 0.8mA. ADJUSTING INITIAL ERRORS Most applications will require adjustment of initial errors. Offset errors can be corrected by adjustment of the zero resistor, RZ. If a low loop supply voltage is used, RL must be made a relatively low value to assure that V+ remains 9V or greater for the maximum loop current of 20mA. It may, in fact, be prudent to design for V+ equal or greater than 9V with loop currents up to 34mA to allow for out-of-range input conditions. The typical performance curve “Loop Resistance vs Loop Power Supply” shows the allowable sense resistor values for full-scale 20mA. Figure 3 shows another way to adjust zero errors using the output current adjustment pins of the XTR103. This provides a minimum of ±300µA (typically ±500µA) adjustment around the initial low-scale output current. This is an output current adjustment which is independent of the input stage gain set MEASUREMENT TEMPERATURE SPAN ∆T (°C) TMIN 100°C 200°C 300°C 400°C 500°C 600°C 700°C 800°C –200°C 18/90 653 18/185 838 18/286 996 18/396 1087 18/515 1131 18/645 1152 18/788 1159 18/946 18/1120 18/1317 1158 1154 1140 900°C 1000°C –100°C 60/84 1105 60/173 1229 60/270 1251 60/374 1249 60/487 1231 60/610 1207 60/746 1181 60/895 60/1061 1155 1128 0°C 100/81 1287 100/167 100/260 100/361 100/469 100/588 100/718 100/860 1258 1229 1201 1173 1145 1117 1089 100°C 138/78 1211 138/162 138/252 138/349 138/453 138/567 138/691 1183 1155 1127 1100 1073 1046 200°C 175/76 1137 175/157 175/244 175/337 175/437 175/546 1110 1083 1056 1030 1003 300°C 212/73 1066 212/152 212/235 212/325 212/422 1039 1013 987 962 400°C 247/71 996 247/146 247/227 247/313 971 946 921 500°C 280/68 930 280/141 280/219 905 881 600°C 313/66 865 313/136 841 700°C 345/64 803 800°C 375/61 743 RZ /RG (Values are in Ω.) RLIN NOTE: Values shown are for a Pt100 RTD. Double (x2) all values for Pt200. TABLE I. RZ, RG, and RLIN Resistor Values for Pt100 RTD. ® 7 XTR103 Figure 4, shows a three-wire RTD connection for improved accuracy with remotely located RTDs. RZ’s current is routed through a third wire to the RTD. Assuming line resistance is equal in RTD lines 1 and 2, this produces a small commonmode voltage which is rejected by the XTR103. (a) XTR103 16 2 OPEN-CIRCUIT DETECTION 1 10kΩ ±500µA typical output current adjustment range. The optional transistor Q2 in Figure 4 provides predictable behavior with open-circuit RTD connections. It assures that if any one of the three RTD connections is broken, the XTR103’s output current will go to either its high current limit (≈34mA) or low current limit (≈3.6mA). This is easily detected as an out-of-range condition. (b) XTR103 16 REVERSE-VOLTAGE PROTECTION 2 1 5kΩ 5kΩ Figure 5 shows two ways to protect against reversed output connection lines. Trade-offs in an application will determine which technique is better. D1 offers series protection, but causes a 0.7V loss in loop supply voltage. This may be undesirable if V+ can approach the 9V limit. Using D2 (without D1) has no voltage loss, but high current will flow in the loop supply if the leads are reversed. This could damage the power supply or the sense resistor, RL. A diode with a higher current rating is needed for D2 to withstand the highest current that could occur with reversed lines. ±50µA typical output current adjustment range. FIGURE 3. Low-Scale Output Current Adjustment. with RG. If the input stage is set for high gain (as required with narrow temperature measurement spans) the output current adjustment may not provide sufficient range. In these cases, offset can be nulled by adjusting the value of RZ. SURGE PROTECTION TWO-WIRE AND THREE-WIRE RTD CONNECTIONS Long lines are subject to voltage surges which can damage semiconductor components. To avoid damage, the maximum applied voltage rating for the XTR103 is 40V. A zener diode may be used for D2 (Figure 6) to clamp the voltage applied to the XTR103 to a safe level. The loop power supply voltage must be lower than the voltage rating of the zener diode. In Figure 1, the RTD can be located remotely simply by extending the two connections to the RTD. With this twowire connection to the RTD, line resistance will introduce error. This error can be partially corrected by adjusting the values of RZ, RG, and RLIN. Equal line resistances here creates a small common-mode voltage which is rejected by XTR103. 13 4 (RLINE) 1 RZ 5 2 RTD Resistance in this line causes a small common-mode voltage which is rejected by XTR103. Q1 15 RG 11 3 V– IN 1.5kΩ RCM 0.01µF 9 8 RLIN *Q2 optional. Provides predictable output current if any one RTD connection is broken: FIGURE 4. Three-Wire Connection for Remotely Located RTDs. ® XTR103 10 V+ XTR103 6 3 IR RG RG Q 2* 2N2222 12 IR V+IN 8 Open RTD Terminal IO 1 ≈ 34mA 2 ≈3.6mA 3 ≈3.6mA 7 0.01µF There are special zener diode types specifically designed to provide a very low impedance clamp and withstand large energy surges. These devices normally have a diode characteristic in the forward direction which also protects against reversed loop connections. As noted earlier, reversed loop connections would produce a large loop current, possibly damaging RL. 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 often reduce or eliminate this interference. Connect these bypass capacitors to the IO terminal as shown in Figure 7. Although the DC voltage at the IO terminal is not equal to 0V (at the loop supply, VPS) this circuit point can be considered the transmitter’s “ground.” RADIO FREQUENCY INTERFERENCE The long wire lengths of current loops invite radio frequency interference. RF can be rectified by the sensitive input circuitry of the XTR103 causing errors. This generally appears as an unstable output current that varies with the position of loop supply or input wiring. 1N4148 D1 Use either D1 or D2. See “Reverse Voltage Protection.” 10 V+ 0.01µF B XTR103 E D2 1N4001 15 RL 11 VPS IO 7 FIGURE 5. Reverse Voltage Protection. NOTE: (1) Zener diode 36V: 1N4753A or General Semiconductor Transorb™ 1N6286A 10 Use lower voltage zener diodes with loop power supply voltages less than 30V for increased protection. V+ XTR103 B E 15 (1) RL 11 IO VPS Maximum VPS must be less than minimum voltage rating of zener diode. 7 FIGURE 6. Over-Voltage Surge Protection. ® 9 XTR103 13 4 RZ 5 RTD IR 10 V+ RG RG 0.01µF 0.01µF 12 IR V+IN B XTR103 6 3 RCM E RG V–IN 0.01µF 15 11 7 9 8 0.01µF RLIN FIGURE 7. Input Bypassing Techniques. +12V 13 12 IR IR 4 V+IN 5 B XTR103 1µF 15 0.01µF 16 E 6 RG 3 V–IN 9 10 3 IO 11 8 RZ 138Ω 100°C to 600°C 10 V+ RG RG 448Ω Pt100 1N4148 11 12 7 VO = 0 to 5V 15 RCV420 RLIN 2 IO = 4-20mA 1.5kΩ 1100Ω 14 13 5 4 1µF 0.01µF –12V FIGURE 8. ±12V-Powered Transmitter/Receiver Loop. 13 12 IR IR 4 V+IN 5 1µF 10 0 V+ RG B XTR103 RG RTD +15V 1N4148 1µF 15 6 RG E IO 11 3 V–IN 7 8 RZ 9 Isolated Power from PWS740 –15V 0.01µF 16 10 3 11 12 2 IO = 4-20mA 1.5kΩ 14 13 4 V+ 1 15 RCV420 RLIN 9 15 ISO122 5 10 7 8 VO 0 – 5V 2 16 V– 0.01µF FIGURE 9. Isolated Transmitter/Receiver Loop. ® XTR103 10