KEI 179A INST 电路图.pdf

Instruction Manual Model 179A TRMS Multimeter 01982, Keithley Instruments, Inc. Cleveland, Ohio, U.S.A. Document Number 32430 RadioFans.CN 收音机爱 好者资料库 SPECIFICATIONS DC AND TRMS AC AMPS 20 A A 0.5%+2d* l%+lEdt 0.5” ,Ornll *Add 0.1 %rdg above 15A fo, self-testing. tlktir max. MAXIMUM INPUT: 24 250” DC o, rms (fuse protected, except or 20A range: l5A continuous. 20A for 1 minute lunfusedl. TEMPERATTURE COEFFlClENT OF-18C Et 28-!XioC,: DC f,O.Ol% +O.Zd,T. AC * lO.O7% +2dlPC. CREST FACTOR Iratio of peak value to rms valuel: 31. SETTLING TIME: DC: 1 second to within 1 digit of final reading. AC: 2 seconds to within 15 digits of final reading. MAXIMUM OPEN CIRCUIT VOLTAGE: 5” GENERAL DISPLAY: Five 0.5” LED digits. appropriate decimal position and polarity indication. CONVERSION PERIOD: 4OOms. OVERRANGE INDICATION: Display blinks all zmoes above 19999 counts. MAXIMVM COMMON MODE VOLTAGE: ,400” oeak. EWI,R,ONMENT: Operating: 0 0 -55C. 0% to 80% relative humidity up c. storage: -25T to +l35oc. POWER : 105-125” 0, 210-250” bvitch selectedl. go-,lO” available. 5060 Hz, 5.5w. Optional B-hour batmy pack. Model 1788. DIMENSIONS. n IEIGHT: 85mm high x 235mm wide x 275mm deco 13%” x 9%” x WY,“,. Netweigirt l.Skg 14 Ix). ACCESSORIES SUPPLIED: ,nst,wtio” Manual md Mode, ,691 Tesf Leads. ACCESSORIES AVAILASLE: Model 1010: Single Rack Mounting Kit Model 1017: Dual Rack Mounting Kit Model 1301: Temperature Probe Model 1600A: High Voltage Probe ,4Ok”, Model 1651: 50.Ampere Current Shunt Model 1581: Clip-On Test Lead Set Model ISSZA: RF Probe Model 1683: Universal Test Lead Kit Model 1584: Herd She, Carwing Case Model ,885: Clamp-On AC Probe Model 1591: General Purpass Test Lead Set Model 1788: Rechargeable Smtery Pack Model 1792: Isolated SCD Output Model 1793: isolated IEEE-488 O”f,uf Model 7008-3: IEEE488 Cable (3 ft.1 Model 7008-6: IEEE-488 Cable 18 tt., RadioFans.CN 收音机爱 好者资料库 TABLE OF CONTENTS PARAGRAPH TITLE PAGE 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 SECTION 1 GENERAL INFORMATION Introduction. . . Features . Warranty Information . . . ManualAddenda. . Safety Symbols and Terms . Unpacking and Inspection . . , . . . . Optional Accessories . Specifications . , . . . . 4.4 4.5 4.5.1 4.5.2 4.6 4.6.1 4.6.2 4.6.3 4.6.4 4.7 4.8 4.9 4.10 2.1 2.1.1 2.1.2 2.1.3 2.2 2.2.1 2.2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 4.1 4.2 4.2.1 4.2.2 4.2.3 4.3 4.3.1 4.3.2 SECTION 2 OPERATION Preparation for Use., . . . LinePower. . Battery Pack Power . . Battery Charging . . . . Operating lnsfructi”ns . , . . Environmental Conditions . . , . Front Panel Familiarization . . . DMMMeasurements . DC Voltage Measurement . . . . TRMS AC Voltage Measurement . . . . Resistance (111 Measurement . . Current Measurement IDC or TRMS ACI . . AC and DC Measurement . . . . . SECTION 3 PERFORMANCE VERIFICATION Introduction. . . . . . Environmental Conditions . . . . Recommended Test Equipment . . . PerformanceVerification Procedure . . . Initial Conditions . , . . . . . DCVoltsVerification . AC Volts Verification . . . . Resistance Verification. . . DC Current Verification . , . . . AC Current Verification . . . . . SECTION 4 THEORY OF OPERATION Introduction., . . , . . Overall Operation . . . Signal Conditianing . . . . . . Ohms Cowersian . . . . . A/D Converter . . . . . Attenuation . DC”o,ts. . AC”“,ts. . 21 21 2-l 2-1 21 2-1 21 2-3 2-3 24 2-4 24 25 3-1 31 3-1 31 31 31 3-2 3-2 3-2 3-2 4-1 41 41 4-1 4 1 42 42 42 . 42 42 4-2 42 43 4-3 43 4-3 4-3 44 4-4 5.1 5.2 5.2.1 5.2.2 5.2.3 5.2.4 5.3 5.4 5.4.1 5.5 5.6 5.7 6.1 6.2 6.3 6.4 6.5 6.6 SECTION 5 MAINTENANCE Introduction., , Calibration Procedure Rccommendcd Tesr Equipment Environmental Canditions Calibration Shield Installation Calibration Adjustments Batten/ Pack iModel 17881 installation Troubleshooting . . Troubleshooting Procedure Special Handling of Static Sen 1200V peak, for lo seconds per minute. 1200V peak. 1OOOV rms; 1400V peak; 107WHz. 2A, 250V DC or rms (fuse protected) 15A continuous, 20A for 1 minute (50% duty cycle1 450V rms sine wave; 1OOOV peak, for lo seconds per minute. Figure 2-4. AC Voltage Measurement 2.3.3 Resistance III) Measurement 1. Select the 12 function. 1. For current measurements up to 20OOmA: A. Select the ACA or DCA function, B. Select the desired range (up to 2000mA). C. Connect the unknown current to the INPUT jacks of 2. Select the HI mode or the LO mode (see paragraph 2.2.2 the Model 179A as shown in Figure 2-6. SteD 31. D. Note reading on display. Figure 2-5. Resistance InI Measurement 2.3.4 Current Measurement IDC or TRMS AC) NOTE To prevent measurement errors, connect the current test leads to either the 20A jacks or the normal INPUT jacks. Disconnect all cir- cuits from the unused jacks. WARNING To prevent electrical shock, remove power from the circuit to be measured before connecting the Model 179A. 3. Connect the unknown resistance (RI to the INPUT jacks 2. FW current measurements between 2000mA and 20A: of the 179A as shown in Figure 2-5. A. Select the ACA or DCA function. 4. Note reading on display. B. Depress the 20A range switch. C. Connect the unknown current to the 20 AMP jacks of the Model 179A as shown in Figure 2.7. D. Note the reading on display. 2-4 Figure 2-6. Current Measurements up to 2006mA NOTE Up to 15A may be applied continuously without degradation of the measurement due to self-heating effects. For currents be- tween 15A and 20A. specified accuracy can only be obtained when measurements are limited to a 50% duty cycle (i.e., apply the current for a maximum of one minute and then allow et least one minute for cooling before the next measurement). NOTE The test leads used must be capable of handling 20A and it is recommended that they be twisted (see Figure 2-71 to minimize external fields which could affect the Model 179A or other equipment. Also, keep the test leads as short es possible to mlnlmlze voltage drop. Figure 2-7. Current Measurements Between 2000mA and 20A 2.3.5 AC + DC Measurement Use the Model 179A to meawre TRMS on ;I sigrw WIWII has both AC and DC components as lollows: 1. Measure and record the TRMS AC cononent as described in paragraph 2.3.2. 2. Measure and record the DC component as descritxxl III paragraph 2.3.1. 3. Compute the rms value from the followim e(/uaton ERMs im 2-512-6 SECTION 3 PERFORMANCE VERIFICATION 3.1 INTRODUCTION Performance verification may be done upon receipt of the instrument to ensure that no damage or misadjustment has occurred during transit. Verification may also be performed whenever there is question of the instruments accuracy and following calibration if desired. NOTE For instruments that are still under warranty (less than 12 months since date of shipment), whose performance falls outside specifications at any point, contact your Keithley representative or the factory imp mediately. 3.2 ENVIRONMENTAL CONDITIONS Measurements should be made at 18-28C and at less than 80% relative humidity. 3.3 RECOMMENDED TEST EQUIPMENT Table 3-l lists all the test equipment required for verifi- cation. If alternate equipment is used, the alternate test equipments specifications must be at least as good as the equipment specifications listed in Table 31. 3.4 PERFORMANCE VERIFICATION PROCEDURE Use this procedure to verify the Model 179As accuracy. If the Model 179A is out of spec. proceed to maintenance (calibration) Section 5, unless the Model 179A is under warranty. NOTE Verification should be performed by qualified personnel using accurate and reliable test equipment. WARNING Some procedures require the use of high voltage. Take care to prevent con- tact with live circuits which could cause electrical shock resulting in injury or death. 3.5 INITIAL CONDITIONS Before beginning the verification procedure, the instrument must meet the following conditions: 1. If the instrument has been subjected to extremes of temperature, allow internal temperatures to stabilize for one hour minimum at the environmental conditions specified in paragraph 3.2. 2. Turn on the 179A DMM and allow it to warm up for ten minutes. The instrument may be operated from either line power or battery pack power. as Ion51 as the battery pack has been fully charged as described m paragraph 2.1.3. 3. Zero the instrument as described in paragraph 2.2.2 stea 7. 3.6 DC VOLTS VERIFICATION 1. Select the DC V function. 2. Connect the DC Calibrator iltem A, Table 311 ro the instrument. 3. Select the 200mV range. and apply positive 1OOmVDC to the DMM. The reading must be within the limits specified in Table 32. 4. Select each remaining range and apply ihe required voltage as specified in Table 32. verify that the reading is within specifications. 5. Repeat all checks with negative voltage. Table 3-l. Recommended Test Equipment for Performance Verification DC Calibrator AC Calibrator Decade Resistor Current Calibrator SPECIFICATION . D.lV, 1v. 1ov. 1oov. 1ooov f 0.002% or zouv .lV, 1v. 1ov. 1oov * .022% 1ooov t .044% 1.9kR. 19k12. 190kI1 1.9MR. lOM12, ,O.Ol% lOO,A, lmA, lOmA. lOOmA, 1A. 10A. +0.03% MFR MODEL Fluke 343A Fluke 5200A Fluke 5215A ESI RS725 Valhalla 2500E 3-l Table 3-Z. DC Voltage Performance Check Table 3-4. Resistance Performance Check 2ov zoov 12oov 200mV lOO.OOmV 99.93 to 100.07 2v 1 .oooov 0.9995 to 1.0005 1o.ooov 9.995 to 10.005 1oo.oov 99.95 to 100.05 1ooo.ov 999.5 to 1000.5 v full scale, ins eluding X10 amplification for the 200mV ranges The TRMS converter outputs a positive DC signal propor tional to the true root mean square AC signal. This DC signal is the AID input. In the ACA mode, shunt voltage is treated as a 200mV signal, Figure 4-2. Attenuation and Ohms Conversion 4.2.2 Ohms Conversion Resistance measurements are made by configuring the ate tenuator as a resistance to voltage converter. Attenuator stage voltage feedback resistors R, function as amplifier in put resistance connected to either O.lV reference lLOt or the l.OV reference (HI). The unknown resistance is con netted as a feedback resistor around the atterwaton amplifier. The resulting voltage applied to the A/D cow verter is proportional to the unknown resistance. 4.2.3 A/D Converter The A/D converter is a large scale integration (LSII ratiometric device. Converter output is a multiplexed five digit binary coded decimal IBCD) number which is equal !(I 4-l the ratio of input voltage to reference voltage. A separate clock circuit supplies a 1OOkHz timing input to the integrated circuit, which also multiplexes the BCD output. Full scale A/D inputs for various ranges and functions are listed in Table 4-l. Table 4-l. Full Scale A/D Inputs DCV DCV ACV DCA ACA 11 200mV 2, 20, 200 1200v All All All HI LO Full Scale A/D Input 200mV 2v 2V 200mV 2v 2v 200mV Reference Voltage O.lV l.OV l.OV O.lV l.OV l.OV O.lV 4.3 ATTENUATION When measuring AC and DC voltages, input signal condi- tioning is provided by inverting amplifier UlOl and addi tional components as described below. 4.3.1 DC Volts Input resistance is set by R102 and R103. During calibration, R103 is adjusted to obtain a total input resistance of 10MIl. Zero adjustments are provided for UlOl since an amplifier output resolution of lO!V is required for LO resistance measurements. 1. On the 2V and 200mV ranges. input HI is connected to the A/D converter through protection resistors R106. R135G and R136. Diode-connected FETs Q106 and Q107 clamp the AID input during overload. 2. On the 20, 200 and 1200 volt ranges, the amount of ate tenuation is selected by switching feedback resistors into the attenuator with relays KlOl, K102 and K103. Gain setting components and attenuation values are listed in Table 4-2. Table 4-2. DC Attenuation and Gain Setting Components 4.3.2 AC Volts R diodes CR103 and CR104 sustain negative overloads. Open circuit voltage is set to less than 5V by R150 and R151 through CR103 and CR105. AID protection in ff is the same as in V except R105 is substituted for R106. 4.6 A/D CONVERTER The A/D converter operates on the dual slope principle. The timing is divided into three periods as described below. Operation with high and low reference voltages is described separately in paragraph 4.6.4. 4.6.1 Auto-Zero The auto-zero period IA. Figure 4-31 is 1OOms in length, which corresponds to 10,000 clock pulses. During this period, reference voltage V, (see paragraph 4.6.4) is stored on capacitor C124. Capacitor Cl17 stores VREF + VOSl -vos2. 4.6.2 Signal-Integrate The -i(rnal-integrate period (6, Figure 4-3) is 1OOms In length, The A/D input is buffered by U104 lsee paragraph 4.6.4) and integrated by U103. Positive signals generate a negative-going ramp at the integrator output (pit, 14,. bvi,iie negative signals produce a positivegoing ramp The level of the integrated signal at the end of the signal-integrate period is proportional to the average of the applied signal during this period. Since signal integration continues for 100ms. the A/D converter exhibits high normal mode iejectlw for AC signals in multiples of 10Hr. paticularly the 50 and 60Hr line frequencies. 4.6.3 Reference-Integrate The referenceintegrate period IC or D, Figure 4 31 is 200ms or 20,000 counts in length. During this period, the ins tegrator is returned to baseline level by applying a reference voltage of a polarity opposite to that of the siyxl. A posltlvegolng ramp is obtained by grounding the Ibl.ffer ins put, while negative going ramp is produced by the integral tion of 2XV, ithal is, V, + the voltage stored on C1241. The time, or number of clock pusles reqGred for dscfiarge is proportional to the signal input. Digital output is from latches within U106 which store the number of clock pulses required for the integrator to return to baseline level. The maximum count during this period is 20,000 which cork responds to a discharge period of 200ms or full scale input. 4.6.4 Reference Voltages Reference voltage VREF rmay be either 1V or O.lV. The voltages are provided by a divider across a temperature compensated rener diode. An operational amplifier on U103 provides the zener with a selfregulating bias. Use of the O.lV r