Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsLinear ICsLinear-IC

XTR112, XTR114

RTD

XTR112

XTR114

–

4-20 mA

LIN

REG

7.5V to 36V

XTR112: I

= 250µA

XTR114: I

= 100µA

XTR112

XTR114

4-20mA CURRENT TRANSMITTERS

with Sensor Excitation and Linearization

FEATURES

● LOW UNADJUSTED ERROR

● PRECISION CURRENT SOURCES

XTR112: Two 250µA

XTR114: Two 100µA

● RTD OR BRIDGE EXCITATION

● LINEARIZATION

● TWO OR THREE-WIRE RTD OPERATION

● LOW OFFSET DRIFT: 0.4µV/°C

● LOW OUTPUT CURRENT NOISE: 30nAp-p

● HIGH PSR: 110dB min

● HIGH CMR: 86dB min

● WIDE SUPPLY RANGE: 7.5V TO 36V

● SO-14 SOIC PACKAGE

APPLICATIONS

● INDUSTRIAL PROCESS CONTROL

● FACTORY AUTOMATION

● SCADA REMOTE DATA ACQUISITION

● REMOTE TEMPERATURE AND PRESSURE

TRANSDUCERS

DESCRIPTION

The XTR112 and XTR114 are monolithic 4-20mA,

two-wire current transmitters. They provide complete

current excitation for high impedance platinum RTD

temperature sensors and bridges, instrumentation am-

plifier, and current output circuitry on a single inte-

grated circuit. The XTR112 has two 250µA current

sources while the XTR114 has two 100µA sources for

RTD excitation.

Versatile linearization circuitry provides a 2nd-order

correction to the RTD, typically achieving a 40:1

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 trans-

mitter is low enough to permit use without adjustment

in many applications. This includes zero output cur-

rent drift, span drift and nonlinearity. The XTR112

and XTR114 operate on loop power supply voltages

down to 7.5V.

Both are available in an SO-14 surface-mount pack-

age and are specified for the –40°C to +85°C indus-

trial temperature range.

1998 Burr-Brown Corporation PDS-1473A Printed in U.S.A. December, 1998

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/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132

–200°C

Pt1000 NONLINEARITY CORRECTION

USING XTR112 and XTR114

Process Temperature (°C)

+850°C

–1

Uncorrected

RTD Nonlinearity

Corrected

Nonlinearity

Nonlinearity (%)

XTR112

XTR114

SBOS101

Summary of content (18 pages)

PAGE 1
® XTR112 XTR114 XTR 114 XTR 112 4-20mA CURRENT TRANSMITTERS with Sensor Excitation and Linearization FEATURES APPLICATIONS ● LOW UNADJUSTED ERROR ● PRECISION CURRENT SOURCES XTR112: Two 250µA XTR114: Two 100µA ● RTD OR BRIDGE EXCITATION ● LINEARIZATION ● TWO OR THREE-WIRE RTD OPERATION ● LOW OFFSET DRIFT: 0.4µV/°C ● LOW OUTPUT CURRENT NOISE: 30nAp-p ● HIGH PSR: 110dB min ● HIGH CMR: 86dB min ● WIDE SUPPLY RANGE: 7.
PAGE 2
SPECIFICATIONS At TA = +25°C, V+ = 24V, and TIP29C external transistor, unless otherwise noted. XTR112U XTR114U PARAMETER CONDITIONS OUTPUT Output Current Equation Output Current, Specified Range Over-Scale Limit Under-Scale Limit: XTR112 XTR114 ZERO OUTPUT(1) Initial Error vs Temperature vs Supply Voltage, V+ vs Common-Mode Voltage vs VREG Output Current Noise: 0.
PAGE 3
ABSOLUTE MAXIMUM RATINGS(1) PIN CONFIGURATION Top View Power Supply, V+ (referenced to IO pin) .......................................... 40V + – Input Voltage, VIN, VIN (referenced to IO pin) ............................ 0V to V+ Storage Temperature Range ....................................... –55°C to +125°C Lead Temperature (soldering, 10s) .............................................. +300°C Output Current Limit ...............................................................
PAGE 4
FUNCTIONAL BLOCK DIAGRAM VLIN XTR112: IR1 = IR2 = 250µA XTR114: IR1 = IR2 = 100µA IR1 12 1 IR2 14 VREG V+ IR2 IR1 11 10 + VIN 13 5.
PAGE 5
TYPICAL PERFORMANCE CURVES At TA = +25°C, and V+ = 24V, unless otherwise noted.
PAGE 6
TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, and V+ = 24V, unless otherwise noted.
PAGE 7
TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, and V+ = 24V, unless otherwise noted. CURRENT SOURCE DRIFT PRODUCTION DISTRIBUTION CURRENT SOURCE MATCHING DRIFT PRODUCTION DISTRIBUTION 40 90 Typical production distribution of packaged units. XTR112 and XTR114 included. Typical production distribution of packaged units. XTR112 and XTR114 included.
PAGE 8
APPLICATION INFORMATION The transfer function through the complete instrumentation amplifier and voltage-to-current converter is: Figure 1 shows the basic connection diagram for the XTR112 and XTR114. The loop power supply, VPS, provides power for all circuitry. Output loop current is measured as a voltage across the series load resistor, RL. IO = 4mA + VIN • (40/RG) (VIN in volts, RG in ohms) where VIN is the differential input voltage.
PAGE 9
A 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 1.3mA for the XTR112 and 1mA for the XTR114. Refer to the typical curve “Under-Scale Current vs Temperature.” range from 7.5V to 36V. The loop supply voltage, VPS, will differ from the applied voltage according to the voltage drop on the current sensing resistor, RL (plus any other voltage drop in the line).
PAGE 10
LINEARIZATION RTD temperature sensors are inherently (but predictably) nonlinear. With the addition of one or two external resistors, RLIN1 and RLIN2, it is possible to compensate for most of this nonlinearity resulting in 40:1 improvement in linearity over the uncompensated output. Table I summarizes the resistor equations for two-wire and three-wire RTD connections. An example calculation is also provided. To maintain good accuracy, at least 1% (or better) resistors should be used for RG.
PAGE 11
XTR112 1% RESISTOR VALUES FOR A THREE-WIRE RTD CONNECTION MEASUREMENT TEMPERATURE SPAN ∆T (°C) TMIN 100°C 200°C 300°C 400°C 500°C 600°C 700°C 800°C 900°C 1000°C –200°C 187/267 48700 61900 604/255 86600 110000 187/536 31600 48700 604/499 49900 75000 187/806 25500 46400 604/4750 33200 59000 187/1050 21500 44200 604/1000 24900 49900 187/1330 17800 41200 604/1270 19600 44200 187/1580 15000 39200 604/1500 15800 40200 187/1820 13000 36500 604/1780 13300 37400 187/2100 11300 34800 604/2050 11500
PAGE 12
A typical two-wire RTD application with linearization is shown in Figure 1. Resistor RLIN1 provides positive feedback and controls linearity correction. RLIN1 is chosen according to the desired temperature range. An equation is given in Figure 1. RCM can be adjusted to provide an additional voltage drop to bias the inputs of the XTR112 and XTR114 within their common-mode input range. In three-wire RTD connections, an additional resistor, RLIN2, is required.
PAGE 13
SAMPLE ERROR CALCULATION FOR XTR112(1) RTD value at 4mA Output (RRTD MIN) RTD Measurement Range Ambient Temperature Range (∆TA) Supply Voltage Change (∆V+) Common-Mode Voltage Change (∆CM) ERROR SOURCE UNADJ. ADJUST. 526 26 100 16 668 0 26 0 0 26 0.2%/100% • 106 25ppm/V • 5V 0.1%/100% • 250µA • 1000Ω/(250µA • 3.8Ω/°C • 200°C) • 106 2000 125 1316 0 125 0 10ppm/V • 5V • 250µA • 1000Ω/(250µA • 3.
PAGE 14
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. If the RTD sensor is remotely located, the interference may enter at the input terminals.
PAGE 15
IREG < 2mA Isothermal Block 5V 12 V+ VLIN 13 OPA277 Type J + VIN 1 IR1 14 IR2 11 VREG V– 4 1MΩ(1) 10 V+ RG 1MΩ RG 1250Ω 0.01µF 3 1N4148 XTR112 XTR114 E RG 9 8 IO 20kΩ 2 1kΩ – VIN 7 IRET 6 50Ω 25Ω B + – IO = 4mA + (VIN –VIN) 40 RG RCM(2) NOTES: (1) For burn-out indication. (2) XTR112, RCM = 3.3kΩ XTR114, RCM = 8.2kΩ FIGURE 6. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold-Junction Compensation.
PAGE 16
12 RLIN1 RLIN2 13 4 1 IR1 VLIN + VIN 1N4148 14 11 IR2 10 VREG V+ 0 RG 1µF XTR112 XTR114 RG 3 +15V 1µF B E RG 9 Q1 –15V 0.01µF 16 10 3 8 11 12 – 2 VIN IRET 2 7 6 13 4 IO = 4mA – 20mA 14 V+ 1 15 RCV420 IO RZ Isolated Power from PWS740 9 15 ISO124 5 10 7 8 VO 0 – 5V 2 16 RTD V– NOTE: A three-wire RTD connection is shown. For a two-wire RTD connection, eliminate RLIN2. RCM 0.01µF FIGURE 8. Isolated Transmitter/Receiver Loop.
PAGE 17
PACKAGE OPTION ADDENDUM www.ti.
PAGE 18
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.