ANALOG DEVICES High Performance, 4-20mA Output Voltage-to-Current Converter MODEL 2B20 FEATURES Complete, No External Components Needed Smal! Size: 1.1 x 1.1" x 0.4 Module Input: 0 to +10V; Output: 4 to 20mA Low Drift: 0.005%/C max: Nonlinearity: 0.005% max (2B820B) Wide Temperature Range: -25C to +85C Single Supply: +10V to +32V Meets ISA Std 50.1 for Type 3, Class L and U, Nonisolated Current Loop Transmitters Economical APPLICATIONS Industrial Instrumentation and Control Systems D/A Converter Current Loop Interface Analog Transmitters and Controllers Remote Data Acquisition Systems GENERAL DESCRIPTION Model 2B20 is a complete, modular voltage-to-current con- verter providing the user with a convenient way to produce a current output signal which is proportional to the voltage input. The nominal input voltage range is 0 to +10V. The out- put current range is 4 to 20mA into a grounded load. Featuring low drift (0.005%/C max, 2B20B) over the ~25C to +85C temperature range and single supply operation (+10V to +32V), model 220 is available in two accuracy grades. The 2B20B offers precision performance with nonlinearity error of 0.005% (max) and guaranteed low offset error of 0,1% max and span error of +0.2% max, without external trims. The 2B20A is an economical solution for applications with lesser accuracy requirements, featuring nonlinearity error of 0.025% (max), offset error of +0.4% (max), span error of t0.6% (max), and span stability of 0.01%/C max. The 2B20 is contained in a small (1.1" x 1.1 x 0.4"), rugged, epoxy encapsulated package. For maximum versatility, two signal input (Vini and Vyn2) and two reference input (REFN; and REFjn2) terminals are provided. Utilizing terminals Vyy1 and REFjn eliminates the need for any external components, since offset and span are internally calibrated. If higher accu- racy (up to 0.01%) is required, inputs Vinz and REF} with series trim potentiometers may be utilized. APPLICATIONS Model 2820 has been designed for applications in process con- trol and monitoring systems to transmit information between subsystems or separated system elements. The 2B20 can serve as a transmission link between such elements of process con- . 2B20 ois yo | VOLTAGE TO CURRENT COMPUTER CONVERTER ae CONVERTER $10. CONTROLLER AMPLIFIER - Vai out RECORDER CONDITIONER ACTUATOR Ru Vets SoM (RECEIVER) v trol system as transmitters, indicators, controllers, recorders, computers, actuators and signal conditioners. In a typical application, model 2B20 may act as an interface between the D/A converter output of a microcomputer based system and a process control device such as a variable position valve. Another typical application of the 2B20 may be as a current output stage of a proportional controller to interface devices such as current-to-position converters and current-to- pneumatic transducers. DESIGN FEATURES AND USER BENEFITS Process Signal Compatibility: To provide output signal com- patibility, the 2B20 meets the requirements of the Instrument Society of America Standard $50.1, Compatibility of Analog Signals for Electronic Industrial Process Instruments for Type 3, Class L and U, nonisolated current loop transmitters. External Reference Use: For increased flexibility, when ratio- metric operation is desired, the 2B20 offers a capability of connecting an external reference (i.e., from multiplying D/A converter) to the REFjjy> terminal. Wide Power Supply Range: A wide power supply range (+10V to +32V dc) allows for operation with either a +12V battery, a +15V powered data acquisition system, or a +24V powered process control instrumentation. TEMPERATURE TRANSDUCERS & SIGNAL CONDITIONERS VOL. Il, 9-15SPECIFICATIONS (typical @ +25C and Vs = +15V, unless otherwise noted) Model 2B20A 2B20B INPUT SPECIFICATIONS Voltage Signal Range (to +10V * Input impedance 10kQ . OUTPUT SPECIFICATIONS Current Output Range! 4 to 20mA * Load Resistance Range* Vg =+12V C to 3502 max . Vg =+15V C to 5002 max * Vg= +24V C to 9502 max * NONLINEARITY (% of Span) +0.025% max +0.005% max ACCURACY Warm-Up Time to Rated Specs 1 minute . Total Output Error @ +25C?4 Offset (Vyy = 0 volts) 0.4% max +0.1% max Span (Vin = +10 volts) 40.6% max 0.2% max vs. Temperature (~25C to +85C) Offset (Vin= 0 volts) +0.01%/C max +0.005%/C max Span (Vjn = +10 volts) 0.01%/C max +0.005%/C max DYNAMIC RESPONSE Settling Time to 0.1% of F.S. for 10V Step 25us . Slew Rate 2.5mA/ps * REFERENCE INPUT Voltage +2.5V de . Input Impedance 10k2 . POWER SUPPLY - Voltage, Rated Performance +15V de * Voltage, Operating Supply Change Effect (% of Span) on Offset on Span Supply Current +10V to +32V de max 40.005%/V 0.005%/V mA + ILoaD TEMPERATURE RANGE Rated Performance Storage ~25C to +85C ~55C to +125C CASE SIZE 1.125 X 1.125" x 0.4" NOTES Specifications same as 2B20A. "Current output sourced into a grounded load over a supply voltage range of +10V to +32V. See Figure 1 for the maximum load resistance value over the power supply range. * Accuracy is guaranteed with no external trim acljustments when REFN is connected to REFQUT. All accuracy is specified as % of output span where output span is 16mMA (+0.1%=+0.016mA output error), 5 Reference input is normally connected to the reference output (+2.5V de). * Optional trim pots may be used for calibration at each supply voltage. Specifications subject to change without notice. VOL. Il, 9-16 TEMPERATURE TRANSDUCERS & SIGNAL CONDITIONERS OUTLINE DIMENSIONS Dimensions shown in inches and (mm). fess (28.7) MAX om 4 0.41 (10.4) MODEL 2B20 MAX l [oz TO 0.04 (1.02) {6 TO DIA . 1.13 (28.7) MAX 1 0.1625 0.1625 (4.12) | fa | | 14.42) MAX "| MAX 0.1 (2.5) GRID BOTTOM VIEW WEIGHT: 106 Grams MATING SOCKET: AC1016 LOAD RESISTANCE RANGE The load resistance is the sum of the resistances of all connected receivers and the connection lines. The 2B20 operating load resistance is power supply dependent and will decrease by 50 ohms for each 1 volt reduction in the power supply. Similarly, it will increase by 50 ohms per volt increase in the power supply, but must not exceed the safe voltage capability of the unit. 1.5k 135k boa 1.25k - ok x 750 = C 3 mT 7 aC omar 2 G 250 + fat \ N 5 10 20 25 30 2. 35 MIN MA POWER SUPPLY (+Vg) Volts _ {Vg -5V) RL MAX= So (9) Figure 1, Maximum Load Resistance vs. Power SupplyApplying the 2B20 PRINCIPLE OF OPERATION The design of the 2B20 is comprised cf high performance op amps, precision resistors and a high stability voltage reference to develop biasing and output drive capability. The 2B20 is designed to operate from a single positive power supply over a wide range of +10V to +32V dc and accepts a single ended, 0 to +10V voltage input. The internal reference has nominal out- put voltage of +2.5V (REF out) and is used to develop 4mA out- put current for a zero volts input when REFjy is connected to REFgur- The output stage of the 2B20 utilizes a sensing resistor in the feedback loop, so the output current is linearly related to the voltage input and independent of the load resistance. There is no minimum resistance for the loads driven by the 2B20; it can drive even a short circuit with no damage to the unit. The maximum resistance of the load as seen by the unit (resistance of the load plus the resistance of the connecting wire) is lim- ited. The maximum external loop resistance, Ri, is given by: .|ts=5_ Ry (82) max = ( x0mA Figure 1 shows the operating region cf the 2B20. The load must be returned to power supply common. The voltage appearing between lout (pin 5) and COM (pin 2) should not exceed Vinax = +Vs 5V. Exceeding this value (up to +32V dc) will not damage the unit, but it will result in a loss of linearity. The basic connections of the 2B20 are shown in Figure 2. Veig | oTO+10V Figure 2. Basic Connections Diagram OPTIONAL CALIBRATION AND TRIM PROCEDURE Model 2B20s factory trimmed offset error is +0.1% max and span error is +0.2% max (2B20B). In most applications, further trimming will not be required. If it is necessary to obtain cali- brated accuracy of up to 0.01%, or, if a high signal source resistance (with respect to 10kS2) introduces calibration error, inputs Vjjz2 and REF)x2 and optional trim pots should be used with Vjy; and REF}x1 open. To perform external trims, connect 50082 potentiometers in series with Vy2 (span trim) and REF,n2 (offset trim) as shown in Figure 3. Adjust span pot, monitoring voltage drop across RLOAD, to obtain an out- put voltage of 5.000V (Iour=20mA) for a +10V input. Next, with 0 volts input, adjust offset pot to obtain 1.000V output (lour=4mA). Check both offset and span and retrim if neces- sary after each adjustment. o Vag, Cea ato rov Figure 3. Model 2B20 Connections Using Optional Offset and Span Trims CONNECTING THE 2B20 FOR 0 TO 10mA OUTPUT The 2B20 may be utilized in applications requiring 0 to 1OmA current output for a 0 to 10V input voltage range. To obtain OmA output for OV input, REFynz (pin 6) and REFyw2 (pin 8) terminals should be left open. A typical output current error for a zero volts input (without trimming) is 0.1mA. The 2B20 span calibration may be adjusted by a 1kQ potentiometer in series with the Vpy2 input. Basic connections of the 2B20 used to obtain a 0 to 10mA output are shown in Figure 4a. +Vs + Vsig ) OTO +10V . Figure 4a. Model 2B20 Connected for 0 to 10mA Output Range CONNECTING THE 2B20 FOR 0 TO 20mA OUTPUT The 2B20 may also be configured for use in applications re- quiring 0 to 20mA output for a 0 to +10 volt input range. REF yy (pin 6) is left open, and REFpy2 (pin 8) is con- nected to Vin, (pin 1) through a 32.4kQ resistor. The typi- cal output current error for OV input (without trimming) is 0.1mA. The 2B20 span may be adjusted by a 2kQ2 po- tentiometer in series with the Vpy2 input to provide 9% FSR adjustment range. Basic connections for 0-20mA oper- ation are shown in Figure 4b. +s, 32.4kQ Dy 2kQ + Vsig 0 to +10V Figure 4b. Model 2B20 Connected for 0 to 20mMA Output Range TEMPERATURE TRANSDUCERS & SIGNAL CONDITIONERS VOL. Il, 9-17OUTPUT PROTECTION In many industrial applications, it may be necessary to protect the 4 to 20mA output from accidental shorts to ac line volt- ages. The circuit shown in Figure 5 can be used for this pur- pose. The maximum permissible load resistance will be lowered by a fuse resistance value when protection circuitry is utilized. FUSE (S.B.} V1BA GE. Rioao VARISTOR V27ZA1 Figure 5. Output Protection Circuitry Connections APPLICATIONS Interfacing Voltage Output D/A Converters: The 2B20 is well suited in applications requiring 4 to 20mA output from D/A converters. The voltage necessary to power the current loop can be derived from the same +15V supply that is used to power the converter. The D/A converter, such as the 12-bit AD DAC80, should be connected for operation on the uni- polar 0 to +10V output range. This is shown in Figure 6. After the load resistor connection has been made, the current loop can be calibrated using the offset and span adjustment potentiometers associated with the 2B20 (or the AD DAC80). First, a digital input code of all ones is loaded into the D/A, and the offset adjustment potentiometer is adjusted for a current output of exactly 4mA. Then, a digital code of all Os is loaded into the D/A, and the span adjustment potentiometer is adjusted for a voltage across the load that corresponds to a current of 20mA -1LSB = 19.9961mA. ADI 923 PWR COM POWER SUPPLY +N +15V 10K Tain aby. -18V (OPT) {loFFseT ap.) WF We AF voms, OF [415V 2a VAN PAYA fs heour 7 13 22 14 [16 |2a | 23 5 7 fa 008 BIT t (MSE) 1 oo 2 AD DACSO 18 (sean'aou J 2820 pigiTat | Your 16 | oTO +10 1 fore JL iweur INPUT I t RL 12 v7 2 G BIT 12 (LS@) Figure 6. AD DAC80 4 to 20mA Current Loop Interface 6 OUTPUT Interfacing Current Output D/A Converters: To interface cur-. rent output D/A converters, such as the AD562, a circuit con- figuration illustrated in Figure 7 should be used. Since the - AD562 is designed to operate with an external +10V reference, the same external reference may be utilized by the 2B20 for ratiometric operation. The output of the AD562 is used to drive the summing junction of an operational amplifier to pro- duce an output voltage. Using the internal feedback resistor of the AD562 provides a 0 to +10V output voltage range suitable to drive the 2B20. OFFSET ADJ. ] id 15 +18 ADB81 tov 30.1% O.1yE O.1uF Joan Ban vl ot. 1008 S+" ADI OPT.) av 6 y de 2 js . +2 BITt og OF 7 Ie 8 Vv ADSE6Z 2820 | yoz0ma ' IGITA 15V ouTPUT Inport Rr * = R 43 An0T Uy eur . BIT 12 fm @ ev LSPAN AD] 1G Figure 7, 12-Bit 4 to 20mA Current Loop Interface Microcomputer Current Loop Interface: Figure 8 shows a typical application of the 2B20 in a multichannel microcom- puter analog output system. When a microcomputer is to con- trol a final control element, such as a valve positioner, servo- mechanism or motor, an analog output board with 4 to 20mA outputs is often necessary. The output boards typically have from one to eight channels, each with its own D/A converter. The 2B20, in a compact package, allows for an easy installation without any additional components and offers a 12-bit system compatible performance. VOLTAGE ouTPUT BUFFERED O/A ~ ~{ ACTUATOR REGISTER a 20m A ORIV OUTPUT + DATA BUS MICRO. COMPUTER Seana | i) 1 ( 1 ( 4 1 a" CONTROL BUFFEREO a _ REMOTE Loci REGISTER CONVENTER B20 RECORDER dureur Figure 8. Microcomputer Analog Output Subsystem ore Pressure Contro} System: In Figure 9, model 2B20 is used in a proportional pressure control system. The 3-15psi working pressure of a system is monitored with a pressure transducer interfaced by the model 2B31 signal conditioner. The high level voltage output of the 2B31 is converted to a 4 to 20mA to provide signal to the limit alarm and proportional control cir- cuitry. A current-to-position converter controlling a motorized valve completes the pressure-control loop. ADI 2835 Vee POWER SUPPLY ADI 1 pal aes O-10v | 7820 | 4-20mA Limir eke ESSURE CONDINONER Verten ALARM C= 3-15 PSI L PROPORTIONAL WORKING CONTROLLER PRESSURE 4 MOTORIZED i VALVE a CURRENT-TO- | m} POSITION CONVERTER | Figure 9. Proportional Pressure Control System 4-20mA Isolated 4 to 20mA Output: For applications requiring up to +1500V dc input to output isolation, consider using Analog Devices model 2B22 isolated voltage-to-current converter. VOL. I, 9-18 TEMPERATURE TRANSDUCERS & SIGNAL CONDITIONERS