ANALOG DEVICES FEATURES Low Cost Single or Multi-Channel Capability Using External Oscillator Isolated Power Supply: 15V dc @ 15mA Low Nonlinearity: 0.05% @ 10V pk-pk Output High Gain Stability: 0.001%/1000 Hours; 0.0075%/C Smalt Size: 1.5 x 1.5 x 0.62 Low Input Offset Voltage Drift: 10uV/C (Gain = 100V/V) Wide Input/Output Dynamic Range: 20V pk-pk High CMV Isolation: 2500V de Continuous Wide Gain Range: 1 to 100V/V APPLICATIONS Ground Loop Elimination in Industrial and Process Control High Voltage Protection in Data Acquisition Systems Biomedical and Patient Monitoring Instrumentation Off-Ground Signal Measurements GENERAL DESCRIPTION Model 286] is a low cost, compact, isolation amplifier that is optimized for single or multi-channel use in data acquisition systems for industrial and medical applications. A single ex- ternal synchronizing oscillator can drive from 1 to 16 model 286)s, or a virtually limitless number of model 286s can be configured using multiple ganged oscillators. The oscillator drive circuit can be supplied by the user of specified in a com- pact, low cost, epoxy encapsulated module, model 281, which also includes a voltage regulator for operation over a wide single voltage range of +8V to +28V. In addition to providing multi-channel operation, this new design features adjustable gain, 1 to 100V/V, dual isolated power, +15V dc @ 15mA, +2500V de off ground isolation (CMV) and 110dB minimum CMR at 60Hz, 5kQ source im- balance, in a compact 1.5 1.5" x 0.6" epoxy encapsulated package. Model 286] achieves a low input noise of 8uV pk-pk (100Hz bandwidth, G = 100V/V), nonlinezrity of 0.05% @ 10V pk-pk output, and an input/output dynamic range of 20V pk-pk. Using modulation techniques with reliable transformer isola- tion, model 286] will interrupt ground loops, leakage paths, and high voltage transients to $5kV pk (10ms pulse), providing de to 1kHz (-3dB) response. WHERE TO USE MODEL 286] Industrial Applications: In multi-channel data acquisition sys- tems, computer interface systems, process signal isolators and high CMV instrumentation, model 286] offers complete gal- vanic isolation and protection against damage from transients and fault voltages. High level transducer interface capability is afforded with model 286]s 20V pk-pk input signal range at a gain of 1V/V operation. In portable multi-channel designs, High CMV, High Performance, Synchronized Isolation Amplifier ee MODEL 286 4 INE) PWR 1 ISY PWR OUT FRaysouctn : wmatse Ue. Fy : sianiat starr cpnorTiowine tg guaroly 4 py vonsoucen SROUND MODEL 2665 PS 1 t t qa i MODEL 286) y 38 38 x - COMMS EH rot rot Yo3 ONT BOL i o > GROUND COMMON MODE VOLTAGE 27OQOVEE MAX 4 CHANNEL, ISOLATED DATA ACQUISITION SYSTEM model 286]s single supply, wide range operation (+8V to +16V) offers simple battery operation. Medical Applications: In biomedical and patient monitoring equipment such as multi-channel VCG, ECG, and polygraph recorders, model 286] offers protection from lethal ground fault currents as well as 5kV defibrillator pulse inputs. Low level bioelectric signal recording is achieved with model 286]s low input noise (8uV pk-pk @ G = 100V/V) and high CMR (110dB, min @ 60Hz). DESIGN FEATURES AND USER BENEFITS High Reliability: Model 286) is a conservatively designed, compact module, capable of reliable operation in harsh envi- ronments. Model 286] hasa calculated MTBF of 392,125 hours and is designed to meet MIL-STD-202E environmental! testing as well as the [EEE Standard for Transient Voltage Protection (472-1974: Surge Withstand Capability). As an additional assurance of reliability, every model 286] is factory tested for CMV and input ratings by application of 5kV pk, 10ms pulses, between input terminals as well as input/output terminals. Isolated Power Supply: Dual 15V de @ 15mA, completely isolated from the input power terminals (+2500V dc isolation), provides the capability to excite floating signal conditioners, front end buffer amplifiers as well as remote transducers such as therrnistors or bridges. Adjustable Gain: A single external resistor enables gain adjust- ment from 1V/V to 100V/V providing the flexibility of apply- ing model 286] in both high-level transducer interfacing as well as low-level sensor measurements. ISOLATION AMPLIFIERS 147SPECIFICATIONS MODEL 286]* GAIN (NON-INVERTING) Range (50kQ Load) 1to 100V/V Formula Gain = 1 [100kQ/ 1kQ+R, (kQ) Deviation from Formula t4% vs. Temperature (0 to +70C)' 0.0075%/C vs. Time +0,001%: 1000 hours Nonlinearity,? #5V Output (G = 1 to 100V/V) -#0.05% Nonlinearity, 10V Output (G = 1 to L00V/V) +0.2% INPUT VOLTAGE RATINGS Linear Differential Range, G = 1V/V +10V min Max Safe Differntial Input Continuous 240V rms Pulse, 10ms Duration, 1 Pulse/i0sec +6500V 9k max Max CMV, Inputs to Outputs ac, 60Hz, 1 Minute Duration Pulse, 10ms Duration, 1 Pulse/10sec With 510kQ in series with Guard Continuous, ac or de CMR, Inputs to Outputs, 60Hz, Rg < 5kQ 2500V rns +2500V 9k max +5000V 9k max +2500V 9k max Balanced Source Impedance 114dB 5kQ Source Impedance Imbalance 110dB iin CMR, Inputs to Guard, 60Hz 1kQ Source Impedance Imbalance 78dB Max Leakage Current, Inputs to Power Common @ 115V ac 60Hz 2.5pA rms max OFFSET VOLTAGE, REFERRED TO INPUT Initial, @ +25C (Adjustable to zero) vs. Temperature (0 to +70C) (5 + 45/G) mV At Gain = 100V/V 10nV/C At Other Gains (1 to 100V/V) (7 + 20/G)V?C vs. Supply Voltage t1mV/% INPUT IMPEDANCE Differential 10 OW 1S OpF Overload 300k2 Common Mode 5 x 10'Q1l20pF INPUT DIFFERENCE CURRENT Initial, @ +25C +7nA mix vs. Temperature (0 to +70C) +0.1nA/C INPUT NOISE (Gain = 100V/V) Voltage 0.05Hz to 100Hz 8uV pk-ok 10Hz to ikHz 3.0uV rns Current 0.05Hz to 100Hz SpA pk-pk FREQUENCY RESPONSE (Gain: 1V/V to 100V/V) Small Signal Bandwidth, -3dB 1.0kHz Slew Rate 25mVips Full Power, 10V pk-pk Output 900Hz Full Power, 20V pk-pk Output 400Hz Recovery Time, to *100KV 200ms RATED OUTPU r Voltage, 50k Load 10V min Output Impedance 1k Output Ripple, 1mHz Bandwidth 20mV pk-pk OSCILLATOR DRIVE INPUT* Input Voltage Input Frequency (8 to 1)V pk-pk 100kHz +5%, max ISOLATED POWER SUPPLY Voltage 415V de Accuracy 0, -6% Current +15mA min Regulation, No Load to Full Load +0, -10% Ripple, 100kHz Bandwidth 200mV pk-pk POWER SUPPLY, SINGLE POLARITY Voltage, Rated Performance +15V dc Voltage, Operating +(8V du to 16V de) Current, Quiescent +13mA TEMPERATURE RANGE Rated Performance 0 to +79C -55C 10 +85C 1.5 x 1.5 x 0.62 Storage CASE DIMENSiONS Gain temperature drift is specified as a percentage of output signal level. 2? Gain nonlinearity is specified as a percentage of output signal span. "Specifications are for mode! 286) when driven by ADI model 281 oscillator circuit (see Figure 12). Specifications subject to change without notice. 148 ISOLATION AMPLIFIERS (typice] @ +25C and Vg = +15V de unless otherwise noted) OUTLINE DIMENSIONS Dimensions shown in inches and (mm). SEE GUARDING TECHNIQUES BELOW =| 110 fk (38.1) MAX 0.62 a 2865 05.7) a8 max 4 0.20 TO 0.25 TRIM 14 (5 TO 6.4) OUT 12 omg | BOTTOM VIEW WEIGHT: 40 Grams --| |= GRID 0.1 (2.54) SHIELDED MOUNTING SOCKET AC1054 COPPER CLAD SHIELD GUARD. FEEDTHROUGH WIRE (H) } 2.85 (72.4) 9 wilt 0.14 DIA HOLE (2 PLACES) PWR COM COPPER CLAD SHIELD GUARD a {H) =z 2 2 g 3 5 | fe GRIO 0.1 (2.54) BOTTOM VIEW WEIGHT: 15 Grams GUARDING TECHNIQUES To preserve the high CMR performance of model 286, care must be taken to keep the capacitance balanced about the in- put terminals. A shield should be provided on the printed cir- cuit board under model 286 as illustrated in the outline drawing above (sceened area). The GUARD (pin 6) must be connected to this shield. This shield is provided with the mounting socket, model AC1054 (solder feedthrough wire to the socket guard pin and copper foil surface.) A recommended guarding tech- nique using model AC1054 is illustrated in Figure 1. Best CMR. performance will be achieved by using twisted, shielded cable to reduce inductive and capacitive pickup. To reduce effective cable capacitance, cable shield should be con- nected ta the common mode signal source by connecting the shield as close as possible to signal low as shown in Figure 1. 1B ANSOUCER Ac1054 MODEL 286) CABLE MOUNTING FLOATING TRANSDUCER -& SOCKET GUARD SIGNAL ' SHIELD log in OF Let Eo OF sync yo ro4 \! | a L _4 1 out Of SHIELD | 3 toap TRANS 9UCER | > >50k{2 o eo GRO JND 281 ( NCT ) 6 7 REQUIRED) | croc, A + Re NOTE 2 wy] Ki, 2500V0C MAX POWER GROUND > NOTE 1. GAIN RESISTOR, R USE BOppm/'C, METAL FILM TYPE Vv, LEAVE TERMINAL 2 OPE: FOR GAIN = Woviv, SHORT TERMINAL 2 TO TERMINAL 1 FOR GAINS FROM tV/V TO 100V/V 100k? GAIN= 1+ ths? | Ry (HED NOTE 2. OPTIONAL GUARD RESISTOR, Ag, REQUIRED ONLY FOR CMV 12600Vpx Rg MAY BE CONVENIENTLY MOUNTED ON AC 1054 MOUNTING SOCKET USING THE STANDOFF PROVIDED (Rg). USE 1/4 WATT, 5% CARBON COMPOSITION TYPE; {ALLEN BRADLEY RECOMMENDED) NOTE 3. output FILTER CAPACITOR C. SELECT TO ROLL-OFF NOISE AND OUTPUT RIPPLE: (e.g. SELECT c 1.5: F FOR dc TO 100Hz BANDWIDTH! F (-34dBt = ____ ern Figure 1. Basic Isolator InterconnectionTHEORY OF OPERATION The remarkable performance of model 286] is derived from the carrier isolation technique which is used to transfer both signal and power between the amplifiers guarded input stage and the rest of the circuitry. The block diagram for model 286] is shown in Figure 2 below. The 320k{2 input protection resistor limits the differential in- put current during periods of input amplifier saturation and also limits the differential fault current to approximately 50uA in case the preamplifier fails. The bipolar input preamplifier operates single-ended (non- inverting). Only a difference bias current flows with zero net bias current. A third wire return path for input bias current is not required. Gain can be set from 1V/V to 100V/V by changing the gain resistor, Rj. To preserve high CMR, the gain resistor must be guarded. Best performance is achieved by shorting terminal 2 to terminal 1 and operating model 286] at again of 100V/V. For powering floating input circuitry such as buffer amplifiers, instrumentation amplifiers, calibration signals and transducers, dual isolated power is provided. High CMV isolation is achieved by the low-leakage transformer coupling between the input pre- amplifier, modulator section and the output circuitry. DC TO IkHz DEYOD H FILTER 12) OUTPUT AA A | | VWAe- | Tk&2 100KS2 t MOD | a1) TRIM DRIVE7J~ I! -4-DEMOD -T: DRIVE INPUT FLT. ! +} 7) Vs cOM | | 9) 6 OSCILLATOR ike +15V I BUFFER osc NPUT 15V 9 6 POWER | L_ 8) COM | | POWER SUPPLY INPUT SHIELD 2 GAIN 1+ ~ 100k$ ween (IVA TO 100V/V) Tkst +R, (k82) Figure 2. Block Diagram Medel 286/ OPTIONAL TRIM ADJUSTMENTS Model 286] can be applied directly to achieve rated perform- ance as shown in Figure 1, on page 2. Additional trim adjust- ment capability for bandwidth, output offset voltage and gain (for gains greater than 100V/V) is easily provided as shown in Figure 3 (below). The OUT and TRIM terminals can be floated with respect to PWR COM up to +50V pk, max offering three- port isolation. The TRIM terminal (pin 11) must be connected to the PWR COM terminal (pin 8) when not used to adjust the output off- set voltage. A O0.1uF capacitor from pin 11 to PWR COM is recommended whenever the TRIM terminal is used. BANDWIDTH ROLLOFF | jyey sy #346) 1 o 2n (iki) ~ 286) 40K: ; LOAD ~O 415V E 20Ks2 B2ke2 20K: [OFFSET VOLTAGE = (8) [ower ft TRIM ADJUST ] | GAIN 200: & rO -15V S 20082 T 40K 5? o = POWER COM Figure 3. Optional Connections: Offset Voltage Trim Adjust, Bandwidth (-3dB) Rolloff and Gain Adjust (G>> 100V/V) INTERELECTRODE CAPACITANCE, TERMINAL RATINGS AND LEAKAGE CURRENTS LIMITS Capacitance: Interelectrode terminal capacitance arising from stray coupling capacitance effects between the input terminals and the signal output terminals are each shunted by leakage resistance values exceeding 50kMQ. Figure 4 illustrates the CMR ratings at 60Hz and 5kQ source imbalance between sig- nal input/output terminals, along with their respective capaci- tance, fe 4 ' Bom , 110d8 MIN PWR ? com *WHEN GUARD TIED TO INPUT COMMON MODE SOURCE o! PWR COM Figure 4. Model 286/ Terminal Capacitance and CMR Ratings Figure 5. Model 286/ Terminal Ratings Terminal Ratings: CMV performance is given in both peak pulse and continuous ac or dc peak ratings. Pulse ratings are intended to support defibrillator and other transient voltages. Continuous peak ratings apply from dc up to the normal full power response frequencies. Figure 5 and Table 1 illustrate model 286] ratings between terminals. SYMBOL | RATING l REMARKS V1 (pulse) 6500VpxK (10ms) Withstand Voltage, Defibrillator V1 (cont.) +240V pms Withstand Voltage, Steady State V2 (pulse) +2500Vpx (10ms) Rc; = 0 Transient V2 (pulse) +5000Vpx (10ms) Rg = 510kQ] Isolation, Defibrillator V2 (cont.) +2500VpK Isolation, Steady State V3 (cont.) t50VpK Isolation, de Z1 50kMQ1||20pF Isolation Impedance I 50uUA rms Input Fault Limit, de to 200kHz Table 7. ltsolation Ratings Between Terminals Leakage Current Limits: The low coupling capacitance between inputs and output yields a ground leakage current of less than 2.5uA rms at 115V ac, 60Hz (or 0.02UA/V ac). As shown in Fig- ure 6, the transformer coupled modulator signal, through stray coupling, also creates an internally generated leakage current of about 5uA rms @ 100kHz. Line frequency leakage current levels are unaffected by the power on or off condition of model 286]. For medical applications, model 286J is designed to improve on patient safety current limits proposed by F.D.A., U.L., A.A.M.L and other regulatory agencies (e.g., model 286J com- plies with leakage requirements for the Underwriters Labora- tory STANDARD FOR SAFETY, MEDICAL AND DENTAL EQUIPMENT as established under UL544 for type A and B patient connected equipment reference Leakage Current, paragraph 27.5). In patient monitoring equipment, such as ECG recorders, model 286] will provide adequate isolation without exposing the patient to potentially lethal microshock hazards. Using passive components for input protection, this design limits input fault currents even under amplifier failure conditions. ISOLATION AMPLIFIERS 149TEST CIRCUITS & MAX CURRENT LIMITS FOR ANY SWITCH CLOSURE COMBINATION -S ee }-2 +15V IGOKHz - > 4 7 yee of input rms (M iM 500: C INTERNALLY a a . GENERATED TEST {I} vo ne BY [0 } 100kHz woo - . 286) men rms (mt) it f2s00e 4 I ~] LINE INDUCED Ssgvnc. eons ~ TISVAC, 6OHZ TEST (tlh 10mA 1 - CI 4 i | : 2 | ima. t L f......| _.. 6 ! 4 REJECT ACCI-PT 2 vO REGION REGION 2 2 ; N a & 100HA4. : | wf ane a 6 : : 2 UL & AAMI - ase | 4 ws Pe Con YY INTERNALLY GENERATED g arty Foup) | LEAKAGE CURRENT x 0p A+ +__ --- - it 6 4 4 286J LINE INDUCED LEAKAGE 2 CURRENT WAT a 6 | Hl M=SuA rms 4 TL: 2.5 pA 2 @ 60H, NSVAC @ 100kH2 oO wa | (MAX) | (typ) \ 10 100 1k 10k 100k 1M Figure 6. Model 286/ Leakage Current Performance from Line Induced and Internally Generated (Modulator) Operating Conditions PERFORMANCE CHARACTERISTICS Common Mode Rejection: Input-to-Output CMR is dependent on source impedance imbalance, signal frequency and amplifier gain. CMR is rated at 115V ac, 60Hz and 5kS&2 imbalance at a gain of 100V/V. Figure 7 illustrates CMR performance as a function of signal frequency. CMR approaches 156dB at de with source imbalances as high as 5kQ. As gain is decreased, CMR is reduced. At a gain of 1V/V CMR is typically 6dB lower than at gain of 100V/V. 160 140 = GUARANTEED CMR @G 100V/V 1008 MIN @ 60Hz 8 fp _WITH Skit SOURCE IMBALANICE \ Z 120 - ON at Pa pt & - ) our 8 Cc 9 100 - ~ ~ a 3 ae RN o - : w 80 ta LOIN on 2 paw 8 2 z Co ke ary 2 40 - - - -l 5 Oo 20 TEST cincurt Ski? EACH RESISTOR CMR VALUE GIVEN FOR WORST CASE RESISTOR C: DMBINATION oF 100 1000 10k FREQUENCY ~ Hz Figure 7. Common Mode Rejection vs. Frequency Figure 8 illustrates the effect of source imbalance on CMR per- formance at 60Hz at gains of 1V/V, 10V/V, and 100V/V. CMR is typically 140dB at 60Hz and a balanced source. CMR is maintained greater than 80dB for source imbalances up to 100kQ. 140 s+ GAIN. 100V/V GUARATITEED CMR @G - 100V/V 110dB MIN @ 60H: AND 5ks? SOURCE IMPEDANCE IMBALANCE GAIN 10V/V 2 T | Ss 120 t t iN z 2 GAIN = W/V o 5 4 S wo I | J e Sa SN w ~~ 8 ~ = wo tr * aed 2S WE 2 5 son o o #0 To pyac tut ror 1 *TEST CIRCUIT EACH RESISTOR ADJUSTED 112 TO 100k{2. 40 CMR VALUE GIVEN FOR WORST CASE RESISTOR COMBINATION 10 100 Tk 40k 100k SOURCE IMPEDANCE IMBALANCE - {? Figure 8. Common Mode Rejection vs. Source Impedance Imbalance 150 ISOLATION AMPLIFIERS Gain Nonlinearity: Linearity error is defined as the deviation of the output voltage from the best straight line and is speci- fied as a % of peak-to-peak output voltage span, e.g., nonlinear- ity of model 286] operating at an output span of 10V pk-pk +5V) is t0.05% or 5mV. Figure 9 illustrates gain nonlinearity for any output span to 20V pk-pk (10V). 0.20 0.18 NONLINEARITY % of Output Voltage << cs 8s = o eo So = = a 8 8 B 8 &@ 2 3S 8 oO 2 4 6 8 wm 120~4 16 18 20 OUTPUT VOLTAGE - Voltsp.p Figure 9<. Gain Nonlinearity vs. Output Voltage Input Voltage Noise: Voltage noise, referred to input, is de- pendent on gain and bandwidth as illustrated in Figure 10. RMS voltage noise is shown in a bandwidth from 0.05Hz to the frequency shown on the horizontal axis. The noise in a bandwidth from 0.05Hz to 100Hz is 8uV pk-pk at a gain of 100V/V. This value is derived by multiplying the rms value at f = 100Hz shown in Figure 10 (1.2uV rms) by 6.6. For best noise performance in particular applications, a low pass filter at the output should be used to selectively roll-off noise and undesired signal frequencies beyond the bandwidth of interest (see note 3, Figure 1). Increasing gain will also reduce the input noise. 10 wn | : _ > GAIN = V/V ne ey encore Tl O0V PK-PK IT A (0.05Hz TO 100Hz) 3 | 2 = 10 GAIN = 100V/V BuV PK-PK oO (0.05Hz TO 100Hz) < 44 ' 3 pT one 2 te | re) 2 : 2 V 01 Lt 1 ri 1d L 1 10 100 1000 BANDWIDTH (-3dB) Figure 10. Input Voltage Noise vs. Bandwidth Input Offset Voltage Drift: Total input drift is composed of two sources, input and output stage drifts and is gain depend- ent. The curve of Figure 11 illustrates total input drift over the gain range of 1 to 100V/V. o i > a | e = 5 wu 9 < e a > Eb > z 2 1 10 100 GAIN VV Figure 11. Input Offset Voltage Drift vs. GainREFERENCE EXCITATION OSCILLATOR When applying model 286), the user has the option of building alow cost 100kHz excitation oscillator, as shown in Figure 12, or purchasing a module from Analog Devices model 281. HEX SCHMIT TRIGGER FREQ ADSUST th 3.01ki? [e-9..MM74C14N OR F40014PC Skat SYNC | et [14 | | _-o +15VDC OUT a Ir] 7 12] ip 4a] i a -O G OUT SYNC = ros i a aH 1000pF =~ = (SEE NOTE 3) -{s 10} rte] ot >} 3 |b 7 8 -O @ OUT POWER aa at com {TOP VIEW) NOTES: 1. FREQ. ADJUST: ADJUST TRIM POT FOR OUTPUT FREQUENCY OF 100kHz +5%. 2. FOR SLAVE OPERATION, REMOVE JUMPER FROM SYNC OUT AND SYNC iN PINS. 3. USE CERAMIC CAPACITOR, COG OR NPO CHARACTE 3ISTIC. Figure 12. Model 281 100kHz Oscillator -- Logic and Interconnection Diagram The block diagram of model 281 is showr. in Figure 13. An internal +12V dc regulator is provided to permit the user the option of operating over two, pin selectable, power in- put ranges; terminal 6 offers a range of +14V de to +28V de; terminal 7 offers an input range of +8V dc to +14V de. Wy ev TO +14) +12 +Vg* tay 6 +28) REGULATOR SYNC OUT me SUS Hav o USL 100k Hz 2)6 OUTPUT SYNC IN OSCILLATOR PWR COM 3) @OUTPUT *LEAVE TERMINAL 6 OPEN, WHEN POWER IS APPLIED TO TERMINAL 7 Figure 13. Model 281 Block Diagram Model 2&1 oscillator is capable of driving up to 16 model 286Js as shown in Figure 14. An additional model 281 may be driven in a slave-mode, as shown in Figure 15, to expand the total system channels from 16 to 32. By adding additional model 2&1s in this manner, systems of over 1000 channels may be easily configured. EXTERNAL OSCILLATOR INTERCONNECTION Yup 1 16 i{ ISOLATORS Figure 14. Model 281/286 Connection for Driving from 7 to 16 Isolators 10 286) 10 286 ee Ld > @ > 3]. a}- Si sync al? 4 [ g oe LA 1 out lop TO 16 i UP TO 16 4| sync az | Rove 4] sync {{ ISOLATORS IN of Tin e 281 8 281 a3 286J > Figure 15. Model 281/286 Connection for Driving > 16 !solators TO 284 SYNC IN SPECIFICATIONS (typical @ +25C and Vs = +15V dc unless otherwise noted) MODEL 281 OUTPUT Frequency 100kKHz + 5% Wavetorm Squarewave Voltage (@ and @ terminals) 0 to +12V pk Fan-Out!? 16 max POWER SUPPLY RANGE? High Input, Pin 6 +(14 to 28)V dc Quiescent Current, N.L. +5mA FLL. +16mA Low Input, Pin 7 +(8 to 14)V de Quiescent Current, N.L. +12mA FLL. +33mA TEMPERATURE Rated Performance Storage 0 to 70C -55C to +85C MECHANICAL Case Size Weight 1.4" x 0.6" x 0.49" 10 grams * Model 286) oscillator drive input represents unity oscillator load. ? For applications requiring more than 16 286J's, additional 281s may be used in a master/slave mode. Refer to Figure 15. * Full load consists of 16 model 286]s and 281 oscillator slave. Specifications subject to change without notice. OUTLINE DIMENSIONS Dimensions shown in inches and (mm). MODEL 281 1.4 MAX 2 | (35.6) 0.49 MAX 781 (12.4) 0.20 (5.08) MIN 0.28 (6.35) MAX TT 0.02 (5.2) DIA | 0.6 MAX IE ith =a to | ea _-| C 0.1 (2.54) GRID ke BOTTOM VIEW WEIGHT: 16 GRAMS PIN TERMINAL IDENTIFICATION 1 POWER COMMON 5 SYNC OUTPUT 2 SOUFPUT 6 Vg: HIGH RANGE +(14 to 28)Vy, 3. o OUTPUT 7 #Vg: LOW RANGE 118 to 14)Vy 4 SYNt INPUT MATING SOCKET: CINCH #16 DIP OR EQUIVALENT GUIDELINES ON EFFECTIVE SHIELDING & GROUNDING PRACTICES @ Use twisted shielded cable to reduce inductive and capact- tive pickup. @ Drive the transducer cable shield, S$, with the common mode signal source, Ec, to reduce the effective cable capacitance as shown in Figure 16 below. This is accomplished by con- necting the shield point S, as close as possible to the trans- ducer signal low point B. This may not always be possible. In some cases the shicld may be separated from signal low by a portion of the medium being measured (e.g. pressure transducer). This will cause a commmon mode signal, E,y, to be generated by the medium between the shield and the sig- nal low. The 78dB CMR capability of model 286J between the input terminals (HI IN and LO IN) and GUARD, will work to suppress the common mode signal, Egy @ Dress unshielded leads short at the connection terminals and reduce the area formed by these leads to minimize in- ductive pickup. ISOLATION AMPLIFIERS 151P.C.CARD SHIELD 286J TRANSDUCER FLOATIN . TRanspucer S SPOATING GUARD _#f CABLE 7 100kHz OSC INPUT TRANSDUCER ; SIGNAL ~ Rs Es Rs Em rr a MEDIUM COMMON MODE OFF GROUND VOLTAGE (TRANSDUCER Ec COMMON MODE TERMINALS A,B,C) VOLTAGE GROUND COMM IN MODE = ee eonme VOLTAGE SYSTEM GROUND Figure 16. Transducer Amplifier Interface GAIN AND OFFSET TRIM PROCEDURE In applying the isolation amplifier, highest eccuracy is achieved by adjustment of gain and offset voltage to minimize the peak error encountered over the selected output voltage span. The following procedure illustrates a calibration technique which can be used to minimize output error. In this example, the output span is +5V to -5V and operation at Gain = 10V/V is desired. 1. Apply eqy = 0 volts and adjust Rg for eg = 0 volts. 2. Apply ep, = +0.500V de and adjust Rg for eg = +5.000V de. 3. Apply epy = -0.500V dc and measure the output error (see curve a). 4. Adjust Re until the output error is one half that measured in step 3 (see curve b). 5. Apply +0.500V de and adjust Rg until tre output error is one half that measured in step 4 (see curve c). OUTPUT ERROR mV 5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 OUTPUT VOLTAGE -- Volts 100kHz OSC INPUT FROM MODEL 281 OSCILLATOR Oo Qo M F 3 < Ww t0K Soo A0 +15V ZERO . A0 -15V 9.14 10k2 isolation to eliminate troublesome ground loop problems. Isolated power outputs and adjustable gain add to the applica- tion flexibility of this model. Figure 18 illustrates how model 286} can be combined with a low drift, wVv/rc max, front-end amplifier, model AD510K, to interface low level transducer signals. Model 286]s isolated 15V de power and front-end guard eliminate ground loops and preserve high CMR (110dB min @ 60Hz). 0.01,F 100kHz osc 499k. 499 3 INPUT +15V + s,s ? ADS10K HI IN 1 4 9 b ey _ 100 gd 7 so 190 & 1GmV $362 100823 7 Os iov O.0tHE wo 2 10ks2 Re Ot 4 250k!) 10082 aR 2865 =F 50k: 0.01.F at GAIN = 20k? ADJUST ZERO 8 ion Jo.we ADJUST | >a > 2008: ta 10kS? +. Figure 18. Input Signal Conditioning Using Isolated Power for Transducer Buffer Amplifier Current Loop Receiver: Model 286] can be applied to measure- ment of analog quantities transmitted via 4-20mA current loops over substantial distances through harsh environments. Figure 9 shows an application of model 286] as a current loop receiver. A 25Q resistor converts the 4-20mA current input from a remote loop to a 100-500mV differential voltage input, which the 286] amplifies, isolates, and translates to a 0 to +5V output level at local system ground. Among the most-helpful characteristics of the 286J in this kind of measureinent are the high common-mode rejection (110dB minimum at 60Hz with 5kQ source unbalance) and the high commor-mode rating (+2500 volts dc). The former means low noise pickup; the latter means excellent isolation and protec- tion agzinst large transients. The high common-mode rejection, permitting relatively low input voltage to be used (0.4V span, : in this case), permits the use of a low current-metering resist- ance, which in turn results in low compliance-voltage loading on the current loop, and therefore permits insertion into exist- ing loops without encountering overrange problems. The gain of 12.5 provides a substantial output span, and the floating out- put permits biasing to a O to 5V range. 252 MEASURING Figure 17. Gain and Offset Adjustment APPLICATIONS IN INDUSTRIAL MEASUREMENT AND CONTROL SYSTEMS Remote Sensor Interface: In chemical, nuclear arid metal proc- essing industries, model 286] can be applied to measure and control off-ground millivolt signals in the presence of +2500Vde CMV signals. In interface applications such as pH control systems or on-line process measurement systems such as pollution monitoring, model 286J offers complete galvanic 152 ISOLATION AMPLIFIERS 4-20mA CURRENT RESISTOR G=1258ViV ZERO ADJUST: ADJU: Loop P 1o0kH2 OSC INPUT E,'= OV WHEN SHIELDED O vsv I=4mA CABLE iar 1aF Pr \ a 20ks1 ! (oTo +5v) te ZERO a - |ADJ. 7.68k2. 10k2 : 2 50k82 SPA\ d Y FIESISTOR ARE I 20k2 ' . { o aw CMV = 2.5kV = MAX -15V Figure 19. Isolated Analog Interface; 4 to 20mA is Converted to O to +5V at the Output, with Up to +2500V of Isolation