Isolated mV/Thermocouple Signal Conditioner 1B51 Overall 1000. 1B

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Isolated mV/Thermocouple Signal Conditioner 1B51 Overall 1000. 1B

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FEATURES Functionally Complete Precision Conditioner High Accuracy Input Offset Tempco: Nonlinearity: 0.025% High CMR: 1000 V/V) High Isolation: 1500 Continuous Input Protection Small Package: 1.0" 2.1" 0.35" Isolated Power Low-Pass Filter Compatible with 1B41 Isolated Conditioner APPLICATIONS Multichannel Thermocouple Temperature Measurement Level Data Acquisition Systems Industrial Measurement Control Systems
Isolated mV/Thermocouple Signal Conditioner 1B51
Overall 1000. 1B51 specified over -25°C +85°C operates over industrial (-40°C +85°C) temperature range.
GENERAL DESCRIPTION
1B51 precision, mV/thermocouple signal conditioner that incorporates circuit design utilizing transformer based isolation automated surface mount manufacturing technology. provides unbeatable combination versatility performance compact plastic package. Designed measurement control applications, specially suited harsh environments with extremely high common-mode interference. Unlike costlier solutions that require separate dc/dc converters, each 1B51 generates input side power, providing true, cost channel-to-channel isolation. Functionally, signal conditioner consists three basic sections: chopper stabilized amplifier, isolation output filter. chopper amplifier features highly stable offset tempco µV/°C resistor programmable gains from 1000. Wide range zero suppression implemented this stage. isolation section complete input output galvanic isolation 1500 continuous using transformer coupling techniques. Isolated power provided ancillary circuits such zero suppression open-input detection. Filtering implemented passive antialiasing filter front two-pole active filter output.
DESIGN FEATURES USER BENEFITS
High Noise Rejection: combination chopper stabilized front with low-pass filter provides high system accuracy harsh industrial environments well excellent rejection Hz/60 noise. Input Protection: input internally protected against continuous application rms. Cost: 1B51 offers very cost channel high performance, isolated, level signal conditioners. Wide Range Zero Suppression: This input referred function convenient null large input offsets. Low-Pass Filter: three pole active filter reduces noise aliasing errors. Small Size: 1B51 package size (1.0" 2.1" 0.35") functional completeness make excellent choice systems with limited board space clearance.
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.
Technology Way, P.O. 9106, Norwood, 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
1B51-SPECIFICATIONS (typical
unless otherwise noted)
OUTLINE DIMENSIONS
Model GAIN Gain Equation Gain Error Gain Temperature Coefficient Gain Nonlinearity OFFSET VOLTAGES Input Offset Voltage Initial, +25°C (Adjustable Zero) Temperature Time, Noncumulative Output Offset Voltage Initial Temperature INPUT OFFSET CURRENT Initial Temperature INPUT BIAS CURRENT Initial +25°C Temperature INPUT IMPEDANCE Power Power INPUT VOLTAGE RANGE Linear Differential Input CMV, Input Output Continuous Continuous, Source Imbalance, 1000 Transient Protection INPUT NOISE Voltage, Source Imbalance RATED OUTPUT Voltage, Load, Current Output Noise, Impedance, FREQUENCY RESPONSE Bandwidth, ISOLATED POWER Voltage, Load Current Regulation, Load Full Load Ripple POWER SUPPLY Voltage, Rated Performance Voltage, Operating Current, Quiescent PSRR ENVIRONMENTAL Temperature Range Rated Performance Operating Storage Relative Humidity CASE SIZE
1B51AN
1B51BN
Dimensions shown inches (mm). ±0.025% (±0.04% max)
ppm/°C 0.035% 0.05% max)
(100 max) µV/°C µV/°C max) µV/month -175 µV/°C (2.5 max) pA/°C (12.5 pA/°C max) pA/°C 1500 2000 IEEE-STD (SWC) 7.5% 13.5 0.1%/V
µV/°C
DESIGNATIONS
Designation PROT ICOM -VISO +VISO GAIN
-25°C +85°C -40°C +85°C -40°C +85°C 95%, +60°C 1.00" 2.10" 0.35" (25.4 53.3 8.9)
NOTES same 1B51AN. graph text. Specifications subject change without notice.
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1B51
Functional Block Diagram
INSIDE 1B51 USING 1B51
Referring functional block diagram, power inputs provide power both output side circuitry power oscillator. power oscillator provides timing information signal demodulator drives power transformer input side power supplies. secondary winding half wave rectified filtered create input side bipolar unregulated supplies. signal input (HI) single-pole filtered noise rejection antialiasing. protection clamps limit voltage PROT Thus, large voltage applied between input common (ICOM) appears mostly across input resistor. chopper stabilized gain stage amplifies differential input voltage with gain external resistors. voltage inverting input chopper stabilized amplifier (LO) should equal input voltage which desired output voltage zero. This true input referred zero suppression function. signal amplitude modulated onto carrier passed through signal transformer synchronous demodulator restores signal baseband. two-pole active pass stage filters clock noise completes three-pole Butterworth filter formed with input pole.
Gain Setting gain 1B51 controlled input side pair user provided resistors (see Figure feedback resistor between required between feedback (FB) gain pin. gain setting resistor connected between gain input side common (ICOM). gain equation
Gains 2-1000 achieved adjusting this ratio. accuracy resistor values must taken into account when calculating initial gain accuracy application. initial accuracy 1B51 must then added resistor errors predict total accuracy. Likewise, ratiometric temperature coefficient gain feedback resistors must added temperature coefficient 1B51 predict total resulting thermal drift. possible trimming potentiometer correct initial gain system gain errors. feedback resistor comprised resistor series with trimming potentiometer, long total resistance remains between Alternatively, gain resistor also adjustable resistor. general, greater trim range, coarser resolution. Zero Suppression Since 1B51 differential input device, true input referred zero suppression accomplished (see Figure voltage reference powered input side power supplies applied terminal. Since transfer function (V(HI input voltage which desired output zero should applied pin. equation
=1.25(R2 /(R1
Figure Input Gain Setting Zero Suppression
drift this input zero suppression voltage appears offset drift, temperature stable reference should used. source impedance terminal should kept below
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1B51
Open Input Detection 1B51 sense open thermocouple broken input line with addition external resistor. connecting resistor between positive negative isolated supply, open input will cause positive negative full-scale output, respectively. preserve normal mode input protection capability 1B51, resistor must able withstand high voltage rating obtained connecting lower value resistors series. Cold Junction Compensation When using thermocouple input 1B51, second thermocouple junction formed terminations thermocouple wires, commonly referred cold junction. measured output voltage sensor voltage generated thermocouple minus voltage generated cold junction. Since thermocouples specified with representing 0°C, would ideal maintain cold junction 0°C. more practical approach involves adding temperature dependent voltage thermocouple signal oppose cold junction effects. This type correction known cold junction compensation. Many different methods commonly used implement cold junction compensation. Usually thermistor semiconductor sensor used generate cold junction voltage. slope
Figure 1B51 Cold Junction Compensation
cold junction voltage must same that thermocouple. Therefore, cold junction compensation depends thermocouple type. Sometimes, cold junction compensation sensor used number thermocouple channels. This accomplished measuring temperature connection block directly, adding appropriate voltage each uncompensated thermocouple channel after gain been taken. cases, cold junction sensor must thermal proximity with connection block. Figure shows monolithic cold junction compensation device used with 1B51. Analog Devices AC1226 measures ambient temperature generates appropriate cold junction voltage several different thermocouple types.
TYPICAL PERFORMANCE CURVES
(@TA
+VIso Ripple Capacitance
+VIso Load
REV.
PRINTED U.S.A.
Gain Temperature
Gain
C1147-10-1/89

Isolated mV/Thermocouple Signal Conditioner 1B51 Overall 1000. 1B

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