Loop-Powered 4-20 Sensor Transmitter AD693 PRODUCT DESCRIPTION
|
|
|
Top Searches for this datasheet
FEATURES Instrumentation Amplifier Front Loop-Powered Operation Precalibrated Input Spans Independently Adjustable Output Span Zero Precalibrated Output Spans: 4-20 Unipolar 0-20 Unipolar Bipolar Precalibrated Interface Reference with Current Available Uncommitted Auxiliary Extra Flexibility Optional External Pass Transistor Reduce Self-Heating Errors
Loop-Powered 4-20 Sensor Transmitter AD693
PRODUCT DESCRIPTION
PRODUCT HIGHLIGHTS
AD693 monolithic signal conditioning circuit which accepts low-level inputs from variety transducers control standard 4-20 two-wire current loop. on-chip voltage reference auxiliary amplifier provided transducer excitation; excitation current available when device operated loop-powered mode. Alternatively, device locally powered three-wire applications when 0-20 operation desired. Precalibrated input spans simple strapping. Other spans from realized with addition external resistors. auxiliary amplifier used combination with on-chip voltages provide precalibrated ranges RTDs. Output span zero also determined strapping obtain standard ranges: 4-20mA, 0-20 Active laser trimming AD693's thin-film resistors result high levels accuracy without need additional adjustments calibration. Total unadjusted error tested every device less than 0.5% full scale +25°C, less than 0.75% over industrial temperature range. Residual nonlinearity under 0.05%. AD693 also allows external pass transistor further reduce errors caused self-heating. transmission low-level signals from RTDs, bridges pressure transducers, AD693 offers cost-effective signal conditioning solution. recommended replacement discrete designs variety applications process control, factory automation system monitoring. AD693 packaged 20-pin ceramic side-brazed DIP, 20-pin Cerdip, 20-pin LCCC specified over -40°C +85°C industrial temperature range. REV.
Information furnished Analog Devices believed accurate reliable. However, responsibility assumed Analog Devices use, infringements patents other rights third parties which result from use. license granted implication otherwise under patent patent rights Analog Devices.
AD693 complete monolithic low-level voltage-tocurrent loop signal conditioner. Precalibrated output zero span options include 4-20 0-20 two- three-wire configurations. Simple resistor programming adds continuum ranges basic input spans. common-mode range signal amplifier input extends from ground near device's operating voltage. Provision transducer excitation includes reference output auxiliary amplifier which configured voltage current output signal amplification. circuit configuration permits simple linearization bridge, RTD, other transducer signals. monitored output provided drive external pass transistor. This feature off-loads power dissipation extend temperature range operation, enhance reliability, minimize self-heating errors. Laser-wafer trimming results unadjusted errors affords precalibrated input output spans. Zero span independently adjustable noninteractive accommodate transducers user defined ranges. precalibrated temperature ranges available with strapping.
Technology Way, P.O. 9106, Norwood, 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD693-SPECIFICATIONS
Model LOOP-POWERED OPERATION TOTAL UNADJUSTED ERROR1, TMIN TMAX CALIBRATION ERROR3 LOOP POWERED OPERATION Zero Current Error4
Input Span Output Span 4-20 with external pass transistor unless otherwise noted.)
Conditions AD693AD/AQ/AE Units
0.25 (See Figure Zero Zero Zero Zero 36V6 (See Figure VSIG Input Span Input Span Input Span Input Span Input Span Input Span Into +500 0.5333 0.2666 0.05 0.03 0.05 0.01 0.02
0.75 +100 +VOP
Full Scale Full Scale µA/°C µV/V µV/V ppm/°C Span Span
Temp. Power Supply Rejection (RTI) Common-Mode Input Range Common-Mode Rejection (RTI) Input Bias Current7 TMIN TMAX Input Offset Current7 Transconductance Nominal Unadjusted Error Common-Mode
0.04 0.06 0.05 0.07 +700
Error Temp. Nonlinearity8 OPERATIONAL VOLTAGE RANGE Operational Voltage, VOP6 Quiescent Current OUTPUT CURRENT LIMIT COMPONENTS ERROR SIGNAL AMPLIFIER9 Input Voltage Offset Temp Power Supply Rejection CONVERTER9, Zero Current Error Power Supply Rejection Transconductance Nominal Unadjusted Error 6.200 REFERENCE9, Output Voltage Tolerance Temp. Line Regulation Load Regulation11 Output Current13
Output Span 4-20
µV/°C µV/V
µA/V ppm/°C µV/V mV/mA
0.2666 0.05 +3.5 +5.0 0.75
IREF Loop Powered, (Figure 3-Wire Mode, (Figure
+3.0
REV.
AD693
Model Conditions AUXILIARY AMPLIFIER Common-Mode Range Input Offset Voltage Input Bias Current Input Offset Current Common-Mode Rejection Power Supply Rejection Output Current Range Output Current Error TEMPERATURE RANGE Case Operating14 Storage AD693AD +VOP Units
+0.5 0.005
TMIN TMAX
+0.01
+150
NOTES Total error significantly reduced (typically less than 0.1%) trimming zero current. remaining unadjusted error sources transconductance nonlinearity. AD693 tested loop powered device with signal amp, converter, voltage reference, application voltages operating together. Specifications valid preset spans spans between Error from ideal output assuming perfect +100°C. Refer Error Analysis calculate zero current error input spans less than forcing differential signal amplifier input sufficiently negative zero current always achieved. operational voltage voltage directly across AD693 (Pin two-wire mode, local power mode). example, (ILOOP two-wire mode (refer Figure 10). Bias currents symmetrical with input signal level flow input pins. input bias current inverting input increases with input signal voltage, Figure Nonlinearity defined deviation output from straight line connecting endpoints input swept over input span. Specifications individual functional blocks components error that contribute that included Loop Powered Operation specifications. Includes error contributions converter Application Voltages. Changes reference output voltage load will affect Zero Current. change voltage reference output will result error value Zero Current. used external excitation, reference should loaded approximately (6.2 common). loop powered mode drawn from reference, however, lower limit output span will increased accordingly. maximum current reference source while still maintaining zero. AD693 tested with pass transistor Specifications subject change without notice. Specifications shown boldface tested production units final electrical test. Results from those tests used calculate outgoing quality levels. specifications guaranteed, although only those shown boldface tested production units.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage Reverse Loop Current Signal Input Range -0.3 Reference Short Circuit Common Indefinite Auxiliary Input Voltage Range Auxiliary Current Output Storage Temperature -65°C +150°C Lead Temperature, Soldering +300°C Junction Temperature +150°C
AD693 CONFIGURATION (AD, Packages)
ORDERING GUIDE
Model AD693AD AD693AQ AD693AE
Package Description Ceramic Side-Brazed Cerdip Leadless Ceramic Chip Carrier (LCCC)
Package Option D-20 Q-20 E-20A
Functional Diagram
REV.
AD693-Typical Characteristics
Figure Maximum Load Resistance Power Supply
Figure Bandwidth Series Load Resistance
Figure Input Current Noise Frequency
Figure Differential Input Current Input Signal Voltage Normalized
Figure Signal Amplifier PSRR Frequency
Figure Input Voltage Noise Frequency
Figure Maximum Common-Mode Voltage Supply
Figure CMRR (RTI) Frequency
REV.
AD693
FUNCTIONAL DESCRIPTION
operation AD693 understood dividing circuit into three functional parts (see Figure First, instrumentation amplifier front-end buffers scales lowlevel input signal. This amplifier drives second section, converter, which provides 4-to-20mA loop current. third section, voltage reference resistance divider, provides application voltages setting various "live zero" currents. addition these three main sections, there on-chip auxiliary amplifier which used transducer excitation.
VOLTAGE-TO-CURRENT (V/I) CONVERTER
converter's inverting input (Pin 12). Arranging zero offset this makes zero signal output current independent input span. When input signal zero, noninverting input Since standard offsets laser trimmed factory, adjustment seldom necessary except accommodate zero offset actual source. (See "Adjusting Zero.")
SIGNAL AMPLIFIER
output transistor section sinks loop current when driven high gain amplifier base. input this amplifier derived from difference outputs matched preamplifiers having gains, This difference caused small large gain, negative feedback through transistor loop current sampling resistor between Boost. signal across this resistor compared input left preamp servos loop current until both signals equal. Accurate voltage-to-current transformation thereby assured. preamplifiers employ special design which allows active feedback amplifier operate from most positive point circuit, IIN. stage designed have nominal transconductance 0.2666 A/V. Thus, signal applied inputs (Pin noninverting; inverting) results full-scale output current current limiter operates follows: output feedback preamp accurate indication loop current. This output compared internal setpoint which backs drive transistor when loop current approaches result, loop AD693 protected from consequences voltage overdrive input.
VOLTAGE REFERENCE DIVIDER
Signal Amplifier instrumentation amplifier used buffer scale input match desired span. Inputs applied Signal Amplifier Pins amplified referred reference output much same level translation occurs converter. Signals from preamplifiers subtracted, difference amplified, result back upper preamp minimize difference. Since preamps identical, this minimum will occur when voltage upper preamp just matches differential input applied Signal Amplifier left. Since signal which applied attenuated across resistors before driving upper preamp, will necessarily amplified version signal applied between Pins changing this attenuation, control span referred Signal Amplifier. illustrate: signal applied results loop current. Nominally, applied offset zero leaving range correspond span. And, since nominal attenuation resistors connected Pins 2.00, input signal will doubled result loop current. Shorting Pins results unity gain permits input span. Other choices span implemented with user supplied resistors modify attenuation. (See section "Adjusting Input Span.") Signal Amplifier specially designed accommodate large common-mode range. Common-mode signals anywhere beyond reference easily handled long sufficiently positive. Signal Amplifier biased with respect requires about volts headroom. extended range will useful when measuring sensors driven, example, auxiliary amplifier which above potential. addition, input stage will continue operate normally with common-mode voltages several hundred negative, with respect common. This feature accommodates self-generating sensors, such thermocouples, which produce small negative normal-mode signals well common-mode noise "grounded" signal sources.
AUXILIARY AMPLIFIER
stabilized bandgap voltage reference laser-trimmed resistor divider provide both transducer excitation well precalibrated offsets converter. When used external excitation, reference should loaded approximately (6.2 common). taps resistor divider correspond respectively, result live zero loop current when connected
Auxiliary Amplifier included AD693 signal conditioning aid. used noninverting applications special provisions provide controlled current output. Designed with differential input stage unbiased Class output stage, amplifier resistively loaded common with self-contained resistor with user supplied resistor. functional element, Auxiliary Amplifier used dynamic bridges arrangements such signal conditioner shown Figure used buffer, amplify combine other signals with main Signal Amplifier. Auxiliary Amplifier also provide other voltages excitation
Figure Functional Flock Diagram
REV.
AD693
reference unsuitable. Configured simple follower, driven from user supplied voltage divider precalibrated outputs AD693 divider (Pins provide stiff voltage output less than level, incorporating voltage divider feedback around amplifier, gain-up reference levels higher than large positive outputs desired, Auxiliary Amplifier output current supply, should strapped either Boost. Like Signal Amplifier, Auxiliary requires about headroom with respect input about difference between voltage which required swing. output stage Auxiliary Amplifier actually high gain Darlington transistor where collector emitter. Thus, Auxiliary Amplifier used converter when configured follower resistively loaded. functions high-impedance current source whose current equal voltage divided load resistance. example, using onboard resistor application voltages, either current source transducer excitation. terminal voltage compliance within Auxiliary Amplifier used, then noninverting input, should grounded.
REVERSE VOLTAGE PROTECTION FEATURE USING EXTERNAL PASS TRANSISTOR
emitter output section, IOUT, AD693 usually connected common negative loop connection (Pins Provision been made reconnect IOUT base user supplied transistor shown Figure This permits majority power dissipation moved chip enhance performance, improve reliability, extend operating temperature range. internal hold-down resistor about connected across base emitter external transistor. external pass transistor selected should have BVCEO greater than intended supply voltage with sufficient power rating continuous operation with current supply voltage. should range should greater than emitter current. Some transistors that meet this criteria 2N1711 2N2219A. Heat sinking external pass transistor suggested. pass transistor option also employed other applications well. example, IOUT used drive connected Common, thus providing local monitor loop fault conditions without reducing minimum compliance voltage.
ADJUSTING ZERO
event reverse voltage being applied AD693 through current-limited loop (limited mA), internal shunt diode protects device from damage. This protection mode avoids compliance voltage penalty which results from series diode that must added reversal protection required high-current loops.
Applying AD693
CONNECTIONS BASIC OPERATION
Figure shows minimal connections basic operation: 0-30 input span, 4-20 output span two-wire, loop-powered mode. used external excitation, reference should loaded approximately (6.2 common).
general, desired zero offset value obtained connecting appropriate precision reference/voltage divider network inverting terminal converter. shown Figure precalibrated taps Pins result zero offsets respectively, when connected voltages which zero operating points negative with respect they each have nominal source resistance While these voltages laser trimmed high accuracy, they require some adjustment accommodate variability between sensors provide additional ranges. adjust zero pulling down selected zero tap, making separate voltage divider drive zero pin. arrangement Figure will give approximately linear adjustment precalibrated options with fixed limits. find proper resistor values, first select desired range
Figure Minimal Connection 0-30 Unipolar Input, 4-20 Output
REV.
AD693
Figure Using External Pass Transistor Minimize Self-Heating Errors
adjustment output current from nominal. Substitute this value appropriate formula below adjustment tap. (1.6 V/IA) V/(15 3.75 similar connection with following resistances adjustments tap. (4.8 V/IA) V/(45 3.75 These formulae take into account tolerance resistance insure minimum adjustment range example, choosing will give zero adjustment range full-scale output. maximum value V/200 V/(15 3.75 1.49
0-to-75 signal 0-to-20 mode). gain this amplifier trimmed 2.00 that input signal ranging from 0-to-30 will drive section produce 4-to Joining (Pins will reduce Signal Amplifier gain one, thereby requiring signal drive full span. produce spans less than external resistor, RS1, connected between nominal value given where desired span. example, change span value required. Since internal, gain setting resistors exhibit absolute tolerance 10%, should provided with range adjustment span must well controlled. spans between resistor should connected between nominal value given
example, change span value
Figure Optional Zero Adjustment Trim Available Also)
These rounded down more convenient values which will result adjustment range comfortably greater than
ADJUSTING INPUT SPAN
Input Span adjusted changing gain Signal Amplifier. This amplifier provides 0-to-60 signal section produce 4-to-20 output span REV.
required. Remember that this nominal value require adjustment 10%. many applications span must adjusted accommodate individual variations sensor well AD693. span changing resistor should, therefore, include enough adjustment range handle both sensor uncertainty absolute resistance tolerance Note that temperature coefficient internal resistors nominally ppm/°C, that external resistors should comparably stable insure good temperature performance.
AD693
alternative arrangement, allowing wide range span adjustment between ranges, shown Figure calculated values determined from previous formulae. smallest value then placed series with wiper potentiometer shown figure. example, adjust span between calculated 2000 respectively. smaller value, then reduced cover possible ranges resistance AD693 that value place.
1.0024
Figure shows scheme adjusting modified span offset RE4. trim procedure first connect both signal inputs Reference, zero then adjust that flows current loop. This effect, creates divider with same ratio internal divider that sets zero level (-15 with respect long input signal remains zero voltage zero adjust, will remain with respect
Figure Wide Range Span Adjustment
number other arrangements used span long they compatible with pretrimmed noninverting gain two. span adjustment even include thermistors other sensitive elements compensate span sensor. devising your adjustment scheme, remember that should adjust gain such that desired span voltage Signal Amplifier input translates output. Note also that full differential voltage applied converter 4-20 mode, applied inverting input (zero pin) Divider Network applied noninverting input Signal Amplifier. 0-20 mode, total must applied Signal Amplifier. result, total span voltage will larger than that calculated 4-20 output. Finally, external resistance from should made less than unless voltage reference loaded least simple load resistor used meet this requirement value potentiometer desired.) case should resistance from less than Input Spans Between Input spans obtained adding offset proportional output signal into zero converter. This accomplished with resistors adjusted optional trim scheme shown Figure resistor divider formed from output Signal Amplifier modifies differential input voltage range applied converter. order determine fixed resistor values, RE2, first measure source resistance (RD) internal divider network. This accomplished (power supply disconnected) measuring resistance between offset (Pin common (Pin with reference (Pin connected common. measured value, then used calculate following formula:
Figure Adjusting Spans between (RE1 RE2) with Fine-Scale Adjust (RE3 RE4)
After adjusting place desired full scale across signal inputs adjust that flows current loop. attenuated portion input signal added into zero maintain maximum differential. there some small offset input Signal Amplifier, necessary repeat adjustments.
LOCAL-POWERED OPERATION 0-20 OUTPUT
AD693 designed local-powered, three-wire systems well two-wire loops. usual ranges available threewire operation, addition, 0-20 range used. 0-20 convention offers slightly more resolution simplify loop receiver, reasons sometimes preferred. arrangement, illustrated Figure results 0-20 transmitter where precalibrated span 37.5 Connecting will double span Sensor input excitation unchanged from two-wire mode except increase span. Many sensors ratiometric that increase excitation used instead span adjustment. local-powered mode, increases excitation made easier. Voltage compliance terminal also improved; loop voltage permitted fall volts AD693, easing trade-off between loop voltage loop resistance. Note that load resistor, should meter current into IIN, confuse loop current with local power supply current. REV.
AD693
Figure Local Powered Operation with 0-20 Output INTERFACING PLATINUM RTDS Input filtering recommended applications AD693 been specially configured accept inputs from AD693 input signal range. filter network Platinum RTDs (Resistance Temperature Detectors). each input signal amplifier sufficient, shown Referring Figure temperature stable Figure case resistive signal source resistor form feedback network around Auxiliary necessary only capacitors, shown Figure Amplifier resulting noninverting gain RT/100 capacitors should placed close AD693 where temperature dependent resistance RTD. possible. value filter resistors should kept noninverting input Auxiliary Amplifier (Pin minimize errors input bias current. Choose then driven signal from Voltage Divider (Pin point filter high enough compromise When resistance results bandwidth desired signal. time constant amplifier gain causing Signal filter should matched preserve common-mode Amplifier compares this voltage output (Pin rejection. that zero differential signal results. temperature (and therefore, resistance) increases, will likewise increase according gain relationship. difference between this voltage zero degree value drives Signal modulate loop current. AD693 precalibrated such that full 4-20mA output span corresponds 104°C range RTD. (This assumes European Standard 0.00385.) total precalibrated ranges three-wire two-wire) RTDs available using only strapping options shown Table
OPTIONAL INPUT FILTERING
Figure Optional Input Filtering
variety other temperature ranges realized using different application voltages. example, loading Voltage Divider with resistor from (common) will approximately halve original application voltages allow doubling range resistance (and therefore, temperature) required fill standard spans. Likewise,
Table Precalibrated Temperature Range Options Using European Standard AD693 Temperature Range 104°C +211°C Connections
+25°C +130°C +51°C +266°C -50°C +51°C -100°C +104°C
Figure 0-to-104°C Direct Three-Wire lnterface, 4-20mA Output
REV.
AD693
increasing application voltages adding resistance between Pins will decrease temperature span. external voltage divider also used conjunction with circuit shown produce range temperature spans well providing zero output temperature input. example, measuring with respect voltage 2.385 times excitation (rather than times) will result zero input Signal Amplifier when 100°C 138.5 suggested Table temperature span also adjusted changing voltage span Signal Amplifier. Changing gain from example, will halve temperature span about 52°C 4-20mA output configuration. (See section "Adjusting Input Span.") configuration three-wire shown Figure accommodate two-wire sensors simply joining Pins AD693.
INTERFACING LOAD CELLS METAL FOIL STRAIN GAGES
external voltage divider; Aux-Amp then used follower make stiff drive bridge. Similar applications with higher resistance sensors proportionally higher voltage. Finally, accommodate mV/V sensitivity bridge, full-scale span Signal Amplifier must reduced. Using load cell both tension compression with excitation, therefore, dictates that span adjusted substituting expression, /[(30 mV/S) nominal resistance required achieve this span found 61.54 Calculate minimum resistance required subtracting from 61.54 allow internal resistor tolerance AD693, leaving 55.38 (See "Adjusting Input Span.") standard value 54.9 used with potentiometer full-scale adjustment. load cell with precalibrated sensitivity constant used, resultant full-scale span applied Signal Amplifier found multiplying that sensitivity excitation voltage. Figure excitation voltage actually k/62.3 (6.2 0.995
THERMOCOUPLE MEASUREMENTS
availability on-chip Voltage Reference, Auxiliary Amplifier excitation current make easy adapt AD693 variety load cells strain gages. circuit shown Figure illustrates generalized approach which full flexibility AD693 required interface resistance bridge. high impedance transducer bridge directly powered from Reference. Component values this example have been selected match popular standard mV/V sensitivity bridge resistance. Load cells generally made either tension compression, compression only; zero allows operation tension compression mode. optional zero adjustment provided with values selected adjustment range. Because resistance most foil bridges, excitation voltage must exceed available zero current. About derived from Reference
AD693 used with several types thermocouple inputs provide 4-20 current loop output corresponding variety measurement temperature ranges. Cold junction compensation (CJC) implemented using AD592 AD590 external resistors shown Figure From Table simply choose type thermocouple appropriate average reference junction temperature select values RCOMP voltage developed across RCOMP result AD592 µA/K output added thermocouple loop voltage. potentiometer biased provide correct zero adjustment range appropriate divider also translates Kelvin scale AD592 °Celsius. calibrate circuit, thermocouple bath thermocouple simulator adjust potentiometer loop current. span circuit determined matching signal amplifier input voltage range temperature equivalent
Figure Utilizing Auxiliary Amplifier Drive Load Cell, Output
-10-
REV.
AD693
Figure Thermocouple Inputs with Cold Junction Compensation
Table Thermocouple Application-Cold Junction Compensation
AMBIENT TEMP RCOMP COPPER-NICKEL COPPER COPPER-NICKEL 51.7 53.6 40.2 42.2 60.4 64.9 40.2 45.3 TEMP RANGE 546°C 294K 392K 721°C 374K 261K 413°C 243K 392K WITH GAIN 340K 787°C TEMP RANGE 1035°C
POLARITY
MATERIAL IRON CONSTANTAN NICKEL-CHROME NICKEL-ALUMINUM NICKEL-CHROME
TYPE
301K
thermocouple tables referenced example, output properly referenced type thermocouple when junction 1035°C. Table lists maximum measurement temperature several thermocouple types using preadjusted input ranges. More convenient temperature ranges selected determining full-scale input voltages standard thermocouple tables adjusting AD693 span. example, suppose only 300°C span measured with type thermocouple. From standard table, thermocouple output 12.207 since signal amplifier corresponds span output gain more precisely 12.207 4.915 will needed. Using 12.207 span gain resistor formula given "Adjusting Input Span" yields value about minimum from Adding potentiometer will allow ample adjustment range. With connection illustrated, AD693 will give full-scale indication with open thermocouple.
ERROR BUDGET ANALYSIS
Table lists expressions required calculate total error. AD693 tested with load, loop supply
Table III. Contributions Span Offset Error
Contributions Offset Error Error Source Zero Current Error PSRR Power Supply Rejection Ratio CMRR Common-Mode Rejection Ratio Input Offset Current Contributions Span Error Error Source Transconductance Error XPSRR Transconductance PSRR XCMRR Transconductance CMRR Nonlinearity IDIFF Differential Input Current Expression Error Zero IZE/XS (|VLOOP [|RL IZ]) PSRR |VCM CMRR Expression Error Full Scale VSPAN PSRR |VCM VSPAN XCMRR VSPAN IDIFF
Loop-Powered Operation specifications refer parameters tested with AD693 operating loop-powered transmitter. specifications valid preset spans those spans between. section, "Components Error," refers parameters tested individual functional blocks, (Signal Amplifier, Converter, Voltage Reference, Auxiliary Amplifier). These used indication device performance when AD693 used local power mode when adjusted spans less than REV.
Abbreviations Zero Current (usually Output span (usually Input source impedance Load resistance VLOOP Loop supply voltage Input common-mode voltage VSPAN Input span Nominal transconductance
4-20 signal, flowing through metering resistor, modulates power supplyvoltage seen AD693. change voltage causes power supply rejection error that varies with output current, thus appears span error. input bias current inverting input increases with input signal voltage. differential input current, IDIFF, equals inverting input current minus noninverting input current; Figure IDIFF flowing into input source impedance, will cause input voltage error that varies with signal. change differential input current with input signal approximated linear function, then error source impedance approximated span error. calculate IDIFF, refer Figure find value IDIFF/ corresponding full-scale input voltage your application. Multiply IDlFF. Multiply IDIFF source impedance input voltage error full scale.
-11-
AD693
input common-mode voltage expressions below calculate errors deviations from these nominal conditions. total error zero consists only offset errors. total error full scale consists offset errors plus span errors. Adding above errors this manner result error large 0.8% full scale, however, rule, AD693 performs better span offset errors tend worst case. specification "Total Unadjusted Error," (TUE), reflects this gives maximum error full scale point transfer function when device operated preset spans, with external trims. less than error would adding span offset errors worst case. Thus, alternative calculating total error start with those errors that result from operation AD693 with load resistance, loop supply voltage, common-mode input voltage different than specified. (See Example below.)
ERROR BUDGET SPANS LESS THAN
Error necessary error only error budget. Note that span error reduced zero with span trim, leaving only offset nonlinearity AD693.
EXAMPLE
C1050a-9-10/87 PRINTED U.S.A.
AD693 configured 4-20mA loop powered transmitter with input. inputs driven differential voltage common mode with balanced source resistance. loop supply used with metering resistance. (See Table below.) Trimming offset span your application will remove span offset errors except nonlinearity AD693.
Table Example
OFFSET ERRORS PSRR Already included spec VLOOP CMRR CMRR µV/V; -3.1 µV/V 39.5 0.053 22.4 39.6 12.0 Total Additional Error full scale; (39.5 0.2666 A/V)/20 100% SPAN ERRORS XPSRR XCMRR IDIFF Already included spec PSRR µV/V; (|500 µV/V XCMRR 0.06%/V; 0.06%/V VSPAN VSPAN IDIFF/ from Figure Already included 39.5 74.0 0.5% +0.151% 74.0
SPAN
PSRR µV/V; (|24 mA]) µV/V =5.6
33.0
accommodation must made include input voltage offset signal amplifier when span adjusted less than Zero Current Error include input offset voltage contribution signal amplifier gain input offset voltage multiplied gain signal amplifier, must include additional error when signal amplifier gains greater than example, 300K span thermocouple application discussed previously requires 12.207 input span; signal amplifier must adjusted gain approximately loop transconductance 1.333 A/V, 0.2666 A/V). Calculate total error substituting values transconductance span into equations Table done Example error contribution VOS, however, since already included Zero Current
Total Additional Span Error Full Scale Total Additional Error Full Scale;
OFFSET
113.5 0.151% 0.651%
Full Scale; (113.5 0.2666A V)/20 100% Total Unadjusted Error
ADDITIONAL
OUTLINE DIMENSIONS
Dimensions shown inches (mm). D-20 20-Lead Side Brazed Ceramic
Q-20 20-Lead Cerdip
E-20A 20-Terminal Leadless Chip Carrier
-12-
REV.
Other recent searches
P2008A - P2008A P2008A Datasheet
MT90221 - MT90221 MT90221 Datasheet
ICS848004I - ICS848004I ICS848004I Datasheet
FIN224C - FIN224C FIN224C Datasheet
BAS40W - BAS40W BAS40W Datasheet
BAS40W-04 - BAS40W-04 BAS40W-04 Datasheet
AN768 - AN768 AN768 Datasheet
TC647 - TC647 TC647 Datasheet
DS21447 - DS21447 DS21447 Datasheet
Privacy Policy | Disclaimer
© 2012 Datasheet Archive
