Flukeメーカー189の使用説明書/サービス説明書
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® Model 187 & 189 True RMS M ultimeter Users Manual August 2000, Rev.2, 6/02 © 2000, 2002 Fluke Corporation. All rights reserved. Printed in U.S.
Lifetime Li mi ted Warranty Each Fluke 20, 70, 80, 170 and 180 Series DMM will be f ree from defect s in material and work mans hip f or its lif et ime.
i Table of Contents Chapter Title Page 1 Before You Start .......................................................................................................... 1-1 Safety Information................................................................
Model 187 & 189 Users M anual ii Selecting the Range ....................................................................................................... 2-10 Understanding the Display ...........................................................
Contents (continued) iii Measuring AC Current .............................................................................................. 3-18 Measuring DC Current ....................................................................................
Model 187 & 189 Users M anual iv 6 Maintenance ................................................................................................................. 6- 1 Introduction ....................................................................
v List of Tables Table Title Page 1-1. Safety Information......................................................................................................... ........ 1-2 1-2. International Electrical Sym bols ....................................
Model 187 & 189 Users M anual vi.
vii List of Figures Figure Title P age 2-1. AC Volts Dis play ................................................................................................................... 2-2 2-2. Rotary Switch ..................................................
Model 187 & 189 Users M anual viii 3-10. Temperature Measurem ent ................................................................................................... 3-15 3-11. AC Current Measurement................................................
1-1 Chapter 1 Before You Start Safety Informa tion The Fluke Model 187 and M odel 189 True RMS Multimeters (hereafter referred to as the “ meter ” ) comply with: • EN61010.
Model 187 & 189 Users M anual 1-2 Table 1-1. Safety Information W Warning To avoid possible electric shock or personal injury, follow these guidelines: • Do not use the meter if it is damaged. Before you use the meter , inspect the case. Look for cracks or missing plastic.
Before You Start Safety Information 1 1-3 Table 1-1. Safety Information (cont.) W Warning • When using the probes, keep your fingers behind the finger guar ds on the probes. • Connect the common test lead before you connect the live test lead. When you disconnect test leads, disconnect the live test lead first.
Model 187 & 189 Users M anual 1-4 Symbols Symbols used on the meter and in this manual are explained in Table 1-2. Table 1-2. International Electrical Symbols AC (Alternating Current) Earth ground.
2-1 Chapter 2 Getting Acquainted Introduction Although this manual des cribes the operation of both Models 187 and 189, all illus trations and exam ples assum e use of Model 189.
Model 187 & 189 Users M anual 2-2 tc031f. eps Figure 2-1. AC Volts Display Battery Considerations The meter uses four AA alkaline batteries. The following paragraphs desc ribe several tec hniques used to c onserve battery power.
Getting Acquainted Battery Considerations 2 2-3 Automatic Backligh t Off Press T to select the back light level (low, high, or off.) In low or high, the backlight turns off automatically after a given period. This period is also preset to 15 m inutes and can be set to a m aximum of 99 m inutes from the s etup menu.
Model 187 & 189 Users M anual 2-4 Rotary Switch Turn the meter on by s electing any m easurement function (identified with white letters around the rotary s witch). The meter presents a standard display for that func tion (range, measurem ent units, modifiers, etc.
Getting Acquainted Pushbuttons 2 2-5 Pushbuttons The buttons activ ate features that augment the func tion selected with the rotary switc h. The buttons are shown in Figure 2-3 and described in Table 2-2. Use the blue button ( % ) to acc ess func tions labeled in blue for some of the rotary s witch pos itions.
Model 187 & 189 Users M anual 2-6 Table 2-1. Rotary Switch Selections Position Rotary Switch Function % Blue Key Function AC voltage meas urement from 0 V to 1000.0 V dB over AC, AC over dB , AC millivolt m easurement from 0 mV to 3000.0 mV dB over AC, AC ov er dB $ DC voltage m easurement from 0 V to 1000.
Getting Acquainted Pushbuttons 2 2-7 Table 2-1. Rotary Switch Positions (cont.) Position Rotary Switch Function % Blue Key Function I AC current meas urements from 0 mA to 20.000 A none = AC current meas urements from 0 µ A to 5000.0 µ A none K DC current m easurements from 0 mA to 20.
Model 187 & 189 Users M anual 2-8 Table 2-2. Pushbuttons Button Description Yellow Button Function Description Note Press O to access “Yellow Button Functions .” The O box and the 24-hour clock appear in the lower corners of the display and the prim ary display freezes, allowing tim e to press a s econd button.
Getting Acquainted Pushbuttons 2 2-9 Table 2-2. Pushbuttons (cont.) Button Description Yellow Button Function Description [ • In Setup, increment a digit . • In counter functions , select pos itive pulse s lope. • In ohms c ontinuity, selec t beep on open.
Model 187 & 189 Users M anual 2-10 Selecting the Range Press R to select either a fixed range or the autorange feature. Note You cannot use R in c onductance, diode test, and temperature func tions or with the REL, MIN MAX, and FAST M N MX features.
Getting Acquainted Understanding the Dis play 2 2-11 • dB (in ac volts func tions): the dBm or dBV v alue. • REL: the difference between the pres ent reading and a stored reference reading. • Setup: various mes sages (s ee Chapter 5). • Overload c onditions: OL display ed.
Model 187 & 189 Users M anual 2-12 14 16 15 17 8 9 10 11 7 13 5 6 2 4 3 1 12 tc011f. eps Figure 2-4. Display Features.
Getting Acquainted Understanding the Dis play 2 2-13 Table 2-3. Display Features Number Feature Description ~ Continuity test func tion is selected. Bar Graph. In normal operation 0 (zero) is on the left. In Relative %, 0 is in the center, negativ e values are to the left and pos itive to the right.
Model 187 & 189 Users M anual 2-14 Table 2-3. Display Features (cont.) Number Feature Description FAST MIN MAX AVG FAST MN MX m ode is enabled. ( O M ) Minimum reading displayed. Maxim um reading display ed. Average reading display ed. ; Readings are being recorded in m emory (M odel 189 only.
Getting Acquainted Understanding the Dis play 2 2-15 Table 2-3. Display Features (cont.) Number Feature Description AC+DC For dc volts and dc amps functions, reading represents the rms total of ac and dc measurem ents. e , k e M e , Ω : Ohm. The unit of res istance.
Model 187 & 189 Users M anual 2-16 Table 2-3. Display Features (cont.) Number Feature Description 51000 AUTO MANUAL Range. Digits dis play range in use. f MS 88:88 Time Display. Used with HOLD, AutoHOLD, M IN MAX, FAST MN M X (SAVE, and LOGGING Model 189).
Getting Acquainted Using the Input Terminals 2 2-17 Using the Input Terminals All functions ex cept current us e the * and COM inputs. Current func tions use the inputs shown below: • I or K function: Us e A and COM inputs from 400 mA to 20 A. Use m A/ µ A and COM for inputs ≤ 400 mA.
Model 187 & 189 Users M anual 2-18 Using Display Hold Press Q to enter the Display Hold m ode and freeze the present reading and its tim e stamp. New readings now appear in the secondary display. See Figure 2-6. To ex it Display H old mode, press Q again.
Getting Acquainted Using AutoHO LD 2 2-19 Using AutoHOLD W Warning AutoHOLD mode does not capture unstable or noisy readings. Do not use AutoHOLD mode to determine that circuits are without power. To enter AutoHOLD, press OQ (AutoHOLD). AutoHOLD m ode freezes the present reading and its time stamp.
Model 187 & 189 Users M anual 2-20 To exit MIN M AX mode, press O N (CANCEL) or turn the rotary switc h to a different position. Also, M IN MAX mode turns off automatically when a flashing B (low battery condition) oc curs. Note Minimum, maximum , and average values stored in the MIN MAX m ode are lost when the m eter is turned off.
Getting Acquainted Using F AST MN MX 2 2-21 Using FAST MN MX FAST MN MX c an capture transient s ignal events as short as 250 µs, but with dec reased acc uracy; only 3-1/2 display digits are allowed.
Model 187 & 189 Users M anual 2-22 Using HOLD with MIN MAX or FAS T MN MX You can enable the HOLD mode when in the MIN MAX mode is by pressing Q . No further minimum , maximum , or average updates oc cur while the HOLD m ode is enabled. Exit HOLD mode by press ing Q a second tim e.
3-1 Chapter 3 Making Measurements Introduction Chapter 3 explains how to make m easurements . Most measurem ent functions c an be selected by using the rotary switc h. White letters or sy mbols identify primary func tions; blue letters or sy mbols identify alternativ e functions.
Model 187 & 189 Users M anual 3-2 When measuring v oltage, the meter acts like a 10 M Ω (10,000,000 Ω ) impedance in parallel with the c ircuit. This loading effect can c ause meas urement errors in high- impedance c ircuits. In mos t cases , the error is negligible (0.
Making Measurements Measuring Voltage 3 3-3 dB Measurements in AC Volts Functions The two ac volts functions allow you to display readings as deviations in dB (dec ibels) above or below an established level. Set up dB measurem ents with the following procedure: 1.
Model 187 & 189 Users M anual 3-4 dB is calc ulated with the following formula: = Vr Vx dB 10 log * 20 • For dBm, Vr is the v oltage across the referenc e resistanc e at 1 mW. For example, Vr w ould be 0.7746 V with a 600 Ω reference resis tance.
Making Measurements Measuring Voltage 3 3-5 AC over DC DC over AC AC + DC tc024f. eps Figure 3-3. AC and DC D isplay When the meter shows ac over dc or dc over ac , the following other pushbutton func.
Model 187 & 189 Users M anual 3-6 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN MAX HOLD REL % ms Hz RANGE dB dB ac+d.
Making Measurements Measuring Res istanc e 3 3-7 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN MAX HOLD REL % ms Hz RANGE.
Model 187 & 189 Users M anual 3-8 Keep the following in mind when m easuring resis tance: • Because the m eter ’ s test current flows through all possible paths between the probe tips, the meas ured value of a resistor in a c ircuit is often different from the resistor ’ s rated value.
Making Measurements Using Conduc tance for High Res istance Tes ts 3 3-9 Continuity testing prov ides you with both a visual indication of the state enc ountered (usually near 0 resistanc e for a short or OL for an open) and an audible beep when the input is low.
Model 187 & 189 Users M anual 3-10 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN MAX HOLD REL % ms Hz RANGE dB dB ac+.
Making Measurements Using Conduc tance for High Res istance Tes ts 3 3-11 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN M.
Model 187 & 189 Users M anual 3-12 Measuring Capacitance Caution To avoid possible damage to the meter or to the equipment under test, disconnect circuit power and discharge all high-voltage capacitors before measuring capacitance. Use the dc voltage function to confirm that the capacitor is discharged.
Making Measurements Testing Diodes 3 3-13 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN MAX HOLD REL % ms Hz RANGE dB dB .
Model 187 & 189 Users M anual 3-14 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN MAX HOLD REL % ms Hz RANGE dB dB ac+.
Making Measurements Measuring Tem perature 3 3-15 Measuring Temperature To measure tem perature, set up the meter as s hown in Figure 3-10. The meter begins tem perature measurement in the degree units last us ed (Celsius ° C or Fahrenheit ° F). Once you hav e selected the temperature function, you c an change units by pressing the blue button.
Model 187 & 189 Users M anual 3-16 Measuring Current W Warning Never attempt an in-circuit current measurement where the open-circuit potential to earth is greater than 1000 V. You may damage the meter or be injured if the fuse blows during such a measurement.
Making Measurements Measuring Current 3 3-17 3. If you are using the A term inal, set the rotary sw itch to mA/A. If you are us ing the mA/ µ A terminal, s et the rotary switc h to µ A for currents below 5000 µ A (5 mA), or mA/A for c urrents above 5000 µ A.
Model 187 & 189 Users M anual 3-18 The following are some tips for measuring c urrent: • If the display s hows LEAd5 and you are s ure the meter is set up c orrectly, tes t the meter ’ s fu ses as described under "Tes ting the Fuses" in Chapter 6.
Making Measurements Measuring Current 3 3-19 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN MAX HOLD REL % ms Hz RANGE dB .
Model 187 & 189 Users M anual 3-20 Measuring DC Current To measure dc current, set up the meter as shown in Figure 3-12. You can view s eparate dc and ac am ps signal components . • Press % once to display ac current in the primary display and dc current in the sec ondary display (ac over dc).
Making Measurements Measuring Current 3 3-21 MIN MAX HOLD REL % ms Hz RANGE dB dB ac+dc ac+dc ac+dc ac+dc F nS mA mA A mV V mV V OFF C A A A A mA COM V TEMPERATURE A MIN MAX HOLD REL % ms Hz RANGE dB .
Model 187 & 189 Users M anual 3-22 Measuring Frequency Frequency is the number of cycles a si gnal completes each sec ond. The meter measures the frequency of a voltage or current s ignal by counting the number of tim es the signal cros ses a thres hold level each s econd.
Making Measurements Measuring Duty Cyc le 3 3-23 tc026f. eps Figure 3-14. Hz Display The meter beeps to indic ate when a particular pushbutton is not allowed when m easuring frequency . The following are some general rules. • Relative ( D ), Hold ( Q ), and MIN MAX ( M )can be used.
Model 187 & 189 Users M anual 3-24 -Slope Trigger Point +Slope Trigger Point 30% Above Trigger Point 100% -Slope Trigger Point +Slope Trigger Point 70% Below Trigger Point 100% Measures Positive Pulse Measures Negative Pulse tc009f. eps Figure 3-15.
Making Measurements Measuring Puls e Width 3 3-25 To me asur e dut y cycle , set u p th e met er t o mea su re frequency; then pres s N a sec ond time. You can select the lev el the meter uses by press ing [ to trigger on the positive s lope or ] to trigger on the negative slope.
Model 187 & 189 Users M anual 3-26 +Slope Trigger Point Pulse Width Period = Period -Slope Trigger Point Pulse Width Start and Stop on Positive Slope Start and Stop on Negative Slope 1 Frequency tc020f.
Making Measurements Measuring Puls e Width 3 3-27 The meter meas ures pulse width in the 500.00 or 1000.0 ms ranges . To measure puls e width, set up the meter to meas ure frequency; then pres s N two more times .
Model 187 & 189 Users M anual 3-28.
4-1 Chapter 4 Using Memory & Communications Features Introduction Chapter 4 shows you how to use m emory and comm unication features av ailable on the meters. Note Memory, Logging, and Sav e features apply to the 189 only. Types of Memory The meter has two ty pes of memory data: saved readings and logged readings .
Model 187 & 189 Users M anual 4-2 Storing Saved Readings To add the current display ed reading to the saved readings memory , press O R (SAVE). • 5AVEd appears briefly to c onfirm the operation and the index number dis play increm ents by one. • FULL appears if no room is available in the sav ed readings memory (after 100 saves ).
Using Memory & Communications Features Viewing Memory Data 4 4-3 Viewing Memory Data Use the following proc edure to view mem ory data: Note Viewing memory data involves turning the rotary switch from its current func tion. Selections are not retained when you turn the sw itch.
Model 187 & 189 Users M anual 4-4 2 7 3 4 1 5 6 tc035f. eps Figure 4-1. View Display Table 4-1. View Display No. Item Description q arrow icons. Denotes use of [ or ] to select higher or lower index numbers. Z sym bol Hazardous v oltage could be present at inputs.
Using Memory & Communications Features Clearing Memory 4 4-5 Clearing Memory You can clear mem ory in two way s. • First, If the rotary s witch is in the VIEW M EM position, you can pres s the blue button ( % ) to activ ate the CLEAR MEM func tion.
Model 187 & 189 Users M anual 4-6.
5-1 Chapter 5 Changing the Default Settings Introduction The meter allows y ou to change the default operating configuration of the meter by changing setup options made at the factory . Many of thes e setup options affec t general meter operations and are activ e in all functions.
Model 187 & 189 Users M anual 5-2 Table 5-1. Function Specific Setup Selections Selection Precondition Option Choices ( ) Factory Default 000.0 ° C or 000.0 ° F Temperature ( w ) sele cted . Temperature offset adjust 000.0 ° to ± 100.0 ° C ( 180 .
Changing the Default Settings Selecting Setup Options 5 5-3 Table 5-2. Common Setup Selections Selection Option Choices Factory Default bEEP Beeper yE5 or no (flashing) Use to select. yE5 8888 Displ a y dig its 8888 (4) or 88888 (5) Use to select. 88888 bLoFF Backlight time out MM:SS - Us e q to increment or dec rement minute or second v alues.
Model 187 & 189 Users M anual 5-4 Select and edit setup options as follows: • Turn the rotary switc h to a measurem ent function: • Press O T to advance to the next setup option and save the pres ent selection. • Press [ to increase or ] to decrease a v alue.
Changing the Default Settings Adjusting the Temperature O ffset 5 5-5 If necess ary, adjust the temperature offs et until the temperature on the primary display matc hes the temperature indicated by the lag bath thermometer. 1. Press % ( s ) to advance to the nex t digit and press T ( l ) to go back to the prev ious digit.
Model 187 & 189 Users M anual 5-6 Selecting Display Resolution (3 1/2 or 4 1/2 Digits) For most func tions, you c an choose whether the m eter displays the reading in 3-1/2 or 4-1/2 digits. • The 3-1/2 digit setting provides lower resolution with faster respons e time.
Changing the Default Settings Setting the 24-Hour Clock 5 5-7 Setting the 24-Hour Clock The meter uses 24-hour clock readings as time s tamps during HOLD, AutoHOLD , MIN MAX, FAST M N MX, SAVE, and LOGGING operations. Hours and minutes to a maxim um of 23:59 can be s et.
Model 187 & 189 Users M anual 5-8 Returning to Factory Defaults Your meter comes with the setup options pres et at the factory. Thes e factory s ettings are shown in Tables 5-1 and 5-2. You can always return to these settings as follows: 1. Press O T until Fcty appears in the display .
6-1 Chapter 6 Maintenance Introduction This chapter des cribes bas ic operator maintenanc e. For calibration and performanc e test information, order the 187 & 189 Service M anual , PN 1584337. General Maintenance Periodically wipe the c ase with a dam p cloth and mild detergent.
Model 187 & 189 Users M anual 6-2 1 0 0 0 V 400m A FU S ED 10A M A X FU S ED C A T M IN M A X H O L D R E L % m s H z R A N G E d B d B a c + d c a c + d c a c + d c a c + d c F n S mA mA A mV V m.
Maintenance Replacing the Batteries 6 6-3 Replacing the Batt eries Replace the batteries with four AA batteries (NEDA I5A or IEC LR6). W Warning To avoid false readings, which could lead to possible electric shock or personal injury, replace the batteries as soon as the battery indicator ( B ) appears.
Model 187 & 189 Users M anual 6-4 F2 F1 tc037f. eps Figure 6-2. Battery and Fuse Replacement.
Maintenance Replacing the Fuses 6 6-5 Replacing the Fuses W Warning To avoid electrical shock or damage to the meter, only use replacement fuses specified in Table 6-1. Referring to Figure 6-2, examine or replac e the meter ’ s fuses as follows : 1.
Model 187 & 189 Users M anual 6-6 Table 6-1. User-Replaceable Parts Description Reference Designators Part Number Qty Access Door, Battery / Fus e MP14 666446 1 Tilt-Stand MP8 659026 1 Acces sory Mount MP9 658424 1 W Fuse, 0.44 A (44/100 A, 440 mA), 1000 V, FAST F1 943121 1 W Fuse, 11 A,1000 V FAST F2 803293 1 Battery, 1.
7-1 Chapter 7 Specifications Safety a nd Compliances Maximum volt age bet ween any ter m i nal and eart h ground. 1000 V dc or r ms ac Compliances - DUAL RATI NGS Complies wit h IEC 1010-1 t o 1000 V .
Model 187 & 189 Users M anual 7-2 Physical Specifications Display (LCD) Digital: 50000/5000 counts prim ary dis play, 5000 counts s econdary dis play; updates 4/sec ond. Analog: 51 segments , updates 40/sec ond. Operating Temperature − 20 ° C to + 55 ° C Storage Temperature − 40 ° C to + 60 ° C Temperature Coefficient 0.
Specifications Feature Summary 7 7-3 Feature Summary Feature Description Dual Digital Displays Analog Bar Graph Primary: 50,000 counts Secondary: 5,000 count Bar graph: 51 segments , updates 40 times .
Model 187 & 189 Users M anual 7-4 Basic Specifications Function Ranges/Description DC Voltage 0 to 1000 V AC Voltage, true RMS 2.5 mV to 1000 V – 100 k Hz bandwidth Basic Accuracy DC voltage: 0.
Specifications Detailed Accurac y Specific ations 7 7-5 Detailed Accuracy Specifications Accurac y is spec ified for a period of one year after calibration, at 18 ° C to 28 ° C (64 ° F to 82 ° F), with relativ e humidity to 90 %.
Model 187 & 189 Users M anual 7-6 Accuracy Function Range Resolution 45-1 kHz 20-45 Hz 1-20 kHz 20 kHz-100 kHz AC µ A 500.00 µ A 0.01 µ A 0.75 % + 20 1 % + 20 0.75 % + 20 6 % + 40 5,000.0 µ A0 . 1 µ A 0.75 % + 5 1% + 5 0.75 % + 10 2 % + 40 AC mA 50.
Specifications Detailed Accurac y Specific ations 7 7-7 Accuracy Accuracy Dual Display A C or AC+DC 3 Function Range Resolution DC 20 - 45 Hz 45 Hz - 1 kHz 1 kHz- 20 kHz DC mV 50.000 mV 0.001 mV 0.1% + 20 6 % + 40 500.00 mV 0.01 mV 0.03 % + 2 3000.0 mV 0.
Model 187 & 189 Users M anual 7-8 Function Range Resolution Accuracy Resist ance 1 500.00 Ω 0.01 Ω 0.05 % + 10 3 5.0000 k Ω 0.0001 k Ω 0.05 % + 2 50.000 k Ω 0.001 k Ω 0.05 % + 2 500.00 k Ω 0.01 k Ω 0.05 % + 2 5.0000 M Ω 0.0001 M Ω 0.
Specifications Detailed Accurac y Specific ations 7 7-9 Function Ranges Resolution Accuracy Capacitance 2 1.000 nF 0.001 nF 2% + 5 10.00 nF 0.01 nF 1 % + 5 100.0 nF 0.1 nF 1.000 µF 0.001 µF 10.00 µF 0.01 µF 100.0 µF 0.1 µF 1,000 µF 1 µF 10.0 mF 0.
Model 187 & 189 Users M anual 7-10 Function Range Resolution Accuracy Frequency 500.00 Hz 0.01 Hz 1 ± (0.0050 % + 1) 5.0000 kHz 0.0001 k Hz 50.000 kHz 0.001 k Hz 999.99 kHz 0.01 k Hz Duty Cy cle 10.00% to 90.00 % 0.01 % ± ((voltage range/input voltage) X 300 c ounts) 5,6 Pulse Width 499.
Specifications Frequency Counter Sens itivity 7 7-11 Frequency Counter Sensitivity Approximate VAC Sensitivity (RMS Sine Wave) 1 Input Range 15 Hz to 100 kHz 2 500 kHz 2 VAC Bandwidth 3 Approximate VD.
Model 187 & 189 Users M anual 7-12 Input Characteristics Function Input Impedance (Nominal) Volts, mV 10 M Ω , < 100 pF Common Mode Rejection Ratio Normal M ode Rejection DC Volts, m V >100 dB at dc, 50 Hz or 60 Hz ±0.1% >90 dB at 50 Hz or 60 Hz ± 0.
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