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INSTKUCTIW MANUAL
IlUUEL 1YZU
TKWS UPTIUII
Copyright 1981 Keithley Instruments, Inc.
First Printing, July, 1981, Cleveland, Ohio, U.S.A.
Document No. 32000, Kev. A
Table of Contents
Section Page
1. ClENEKAL INFORMATION ............................. l-l
l-l. Introduction. ............................. l-l
l-3. Warranty Information. ......................... l-l
1-5. Manual Addendums. ........................... l-l
l-7. Safety Symbols and Terms. ....................... l-l
l-9. Specifications. ............................ l-l
2. OPERATING INSTRUCTIONS. ........................... 2-1
2-l. Operation in Model 191. ........................ 2-l
2-4. Operation in Model 192. ........................ 2-1
3. MAINTENANCE ................................. 3-l
3-2. Installation in Model 191 ....................... 3-l
3-3. Installation in Model 192 ....................... 3-2
3-4. Performance Verification. ....................... 3-3
3-6. Kecommended Test Equipment. ...................... 3-3
3-7. Environmental Conditions. ....................... 3-3
3-9. Performance Verification Procedure. .................. 3-3
3-11. Initial Conditions. .......................... 3-4
3-13. Calibration .............................. 3-6
3-15. Kecommended Test Equipment. ...................... 3-6
3-17. Environmental Conditions. ....................... 3-G
X-19. Calibration Procedure ......................... 3-6
3-22. Troubleshooting ............................ 3-9
3-24. Troubleshootiny Procedure ....................... 3-9
4. TtiEURY OF UPEKATIUN ............................. 4-l
5. REPLACEABLE PAKTS .............................. 5-l
5-l. General ................................ 5-l
5-3. Ordering Information. ......................... 5-l
5-5. Factory Service ............................ 5-i
5-7. Schematic and Component Layout. .................... 5-l
Model 1920 General Information
SECTION 1. GENERAL INFORMATION
l-l. INTRODUCTION
l-2. The Keithley Model 1920 is a True Root Mean Square (TKMS) AC plug-in option for the
Models 192 and 191. The 1920 enables the 191 or 192 to measure the TKMS value of an AC
siynal. When the 1920 is installed in the Model 192 an ACtUC function is available. The
Model 1920 has four ranges on which an AC siynal can be measured. It is field
installable.
1-3. Warranty Information
l-4. The warranty is yiven on the inside front cover of this manual. If there is a need
to exercise the Warranty, contact the Keithley Representative in your area to determine
the proper action to be taken. Keithley maintains complete repair and calibration
facilities in the United States, West tiermany, tireat Britain, France, the Netherlands,
Switzerland and Austria. Information concerning the application, operation or service of
your instrument may be directed to the applications engineer at any of the above
locations. Check the inside front cover of this manual for addresses.
l-5. Manual Addendums
1-G. Improvements or changes to the instrument that occur after printing of the [manual
will be explained on an addendum which will be attached to the inside back cover.
1-7. Safety Symbols and Terms
l-8. The symbol A on the instrument denotes that the user should refer to the operating
instructions.
The symbol t on the instrument denotes that up to 5UllV may be present on the terminals.
The WARNING used in this manual explains dangers that could result in personal injury
or death.
The CAUTION used in this manual explains hazards that could damage the instrument.
l-9. Specifications
l-10. Uetailed specifications for the Model 1920 are given in Table l-l.
l-l
General Information Model 1920
TABLE 1-l
1920 Specifications
5-l/2 Digit Accuracy, +(% Rdg + Counts), 1 yr 18-28'C
5-l/2 Digit 20-50Hz" DC, 50Hz-lOkHz* lOK-20kHz" 20kHz-lOOkHz**
Range RESOLUTION
2v 1OPV 1% t 100 0.25% t 100 0.35% + 300 1% t 500
2ov lOOld 1% t 100 0.25% t 100 0.35% + 300 1% t 500
2oov 1mV 1% t 100 0.25% + 100 0.35% + 300 1% t 500
7oov 1OmV 1% t 100 0.354: t 100 0.5% + 300 1% t 500
RESPONSE: TRUE RFlS
CREST FACTOR
AC + DC MODE: Add 60 counts to specified accuracy (not wailable in We1 191)
riAxIriuri INPUT: 1OOOV Peak AC + DC, 2 x lo7 V* Hz
SETTLING TIME: 0.5 set to within 0.1% of change in reading
INPUT IMPEDANCE: 211 ohm shunted by less than 5OpF.
TEMP. COEFFICIENT: (O"-18OC and 28"-5O'C): Less than 0.1 x applicable accuracy
specification per "C below 50kHz; 0.2 x for 50kHz to 1OOkHz
3dB BANTMIDTH: 500kHz Typical
CFIRR: Greater than 60dB at 50 and 60Hz (lk ohm unbalanced)
* Above 2000 counts
** Above 20000 counts; 3% + 500 typical below 20000
l-2
Model 1920 Operating Instructions
SECTION 2. OPERATING INSTRUCTIONS
Z-l. Operating Instructions for the rlcdel 1920 installed in the ilodel 191 are as
follows:
2-2. Ilith the ilodel 1920 option, the ilcdel 191 reads AC voltages froln 10 r;licrovolts/digit
to 1000v. The instrument displays the True Koot llean Square (TKilS) value of an AC
voltage. It has a frequency response of 20Hz to 100ktlz.
2-3. The rnaximm reading is 199YYY. Werrange is irdicatcd by (-) l-----, except on
the 1000 volt range. The 700 volt range is selected idith the 1000 volt button. On the
700 volt range, the display can read beyond the rnaxiinuln allobiable input voltage. ilaximun
allobcable input: 1OOOV Peak AC + DC; 2 x lo7 V'Hz. Use the ilodel 191 to lneasure AC
voltage as follobis:
CAUTION
Do not exceed maximum allohcable input voltage. Instrument damage may
occur.
A. Turn the pokier on IJith the UN/OFF pushbutton, ati depress the ACV pushbutton.
8. Select the desired range from the 4 ranges available. The decimal point is positioned
by the range pushbutton.
C. Ensure that the I0JLL pushbutton is out (light off) unless measurements are to be made
as deviations from a preset value.
NOTE
Do not use NULL to zero the range. A small residual zero readirq is
normal. If NULL is used to zero this offset, readings in specified
accuracy range will be low by the offset amount. This is because rms
measurement signals add in a root mean square fashion arrl not
linearly. The NULL function is a linear offset axl not usable in TKllS
measurements.
0. Connect the signal to be measured between the INPUT HI ati LO binjiny posts. The
birding posts accept wires, spade lugs or banana plugs for ease of connectiq the
circuit to be measured. Observe the displayed digits ard decimal point.
2-1
Operating Instructions Model 1920
E. For specified accuracy (pulse widths ,lOns, peak voltage (1.5 x full scale) Figure 2-1
shows the allowable input signal vs. crest factor. The figure illustrates that for a
crest factor of three the displayed reading must be less than 100,000 counts (1V on
the 2V range). So long as the maximum input is not exceeded no damage will result in
crest factors exceeding that shown in Figure2-I, but accuracy will slowly degrade (For
CF >3 but<10 typical accuracy is degraded by (CF-3) x 0.36% arti peak signal must be
less than 5 x full scale for that range).
CF
I I
0 100000 200000
Displayed Counts
Figure 2-l. Crest Factor VS. Displayed Counts
2-4. Operating Instructions for the Model lY20 installed in the Model 192 are as
follows:
2-5. With the Model 1920 option, the Model 192 reads AC voltages from 1 microvolt/digit
to 1ooov. The instrument displays the True Koot Mean Square (TKMS) value of an AC voltage
signal.
2-G. The maximum reading is
Overrange 199999. is indicated by OFLO. Maximum allowable
input is 1OOOV Peak AC f DC; 2 x 107V.Hz. Use the Model 192 to measure AC or AC + DC
voltages as follows:
CAUTION
Do not exceed maximum allowable input voltage. Instrument darnage may
occur.
A. TURN POWER UN with UN/OFF pushbutton.
B. Press the ACV button once to select the ACV (TKMS) function. Press the ACV button
ayain and the 192 will measure the T'KMS value of an AC + UC signal (AC signal
superimposed with a DC level). The ACV and DCV LEDs will light simultaneously when
the AC + UC function is enabled. Pressing the ACV button again will return the 192 to
the ACV function. Pressiny the DC button while in AC t DC returns the 192 the DCV
function.
2-2
UPEKATINti INSTKUCTIUNS IWDEL 1YZU
NOTE
The 14odel 192 will display "NO AC" if ACV is selected without the 1920
or 1910 ACV option. The AC + UC function is available only with C-4
and dbove software and Kev U and above Analoy Board.
C. SELECT KANtiE from the four ranyes available. The decimal point is positioned by the
ranye pushbutton. The 1UOUV ranye is selected with the 2000 button. If the ZUIQ
button is inadvertently pressed when in ACV function, the 192 will set the ranye to
1uuo.
Il. ZEKU OFF unless [measurements are to be made as deviations frown a preset value.
NOTE
Uo not use ZEKU to zero the ranye. A small residual zero readiny is
normal. If LEKU is used, the residual voltaye readiny in specified
accuracy ranye will be low by the amplitude of the zeroed residual
voltaye. This is because rms measurement signals add in a root mean
square fashion and NUT linearly. THe LEKU function is a linear offset
and not usable in TKMS measurelnents.
E. CONNECT IllPUT to be measured between the HI HCV and LO bindiny posts.
F. TAKE KEAUING.
ti. For specified accuracy (pulse widths LlUus, peak voltage (1.5 x full scale) Figure Z-l
shows the allowable input siynal vs. crest factor. The figure illustrates that for d
crest factor of three the displayed readiny (must be less than lUU,UUU counts (1V on
the ZV ranye). So long as the maximum input is not exceeded no damage will result in
crest factors exceediny that shown in Fiyure 2-1, but accuracy will slowly degrade
(For CF >3 but 510 typical accuracy is degraded by (CF-3) x U.3GX and peak signal must
be less than 5 x full scale for that range).
Model 1920 Maintenance
SECTION 3. MAINTENANCE
3-l. The Model 1920 is a plug-in option that can be installed in your Model 191 or 192
Instdllation of the 1920 into your instrument is as follows.
WARNING
All service information is intended for qualified electronic maintenance
personnel only.
3-2. INSTALLATION: (For use with Model 191)
A. Disconnect the line power cord of the Model 191 and remove all test leads from its
input terminals for safety.
B. Turn the DMM bottom side up and loosen the four screws in the bottom cover.
C. Hold the top and bottom cover together to prevent their separation and turn the DMM
over to the normal position. Remove the top cover.
D. Remove the RF shield by grasping it and FIRMLY lifting it away from the motherboard.
E. Carefully insert the connector of the 1920 into its mating receptacle on the 191
motherboard. Take note of the orientation of the 1920 into the 191 motherboard as
shown in the figure below. Connect the brown wire of the 1920 to Pin 7 of the DCV
switch, and connect the blue wire to Pin 9 of the ACV switch.
F. Replace the RF shield being careful not to pinch any wires.
G. Calibrate the 1920 per the procedure located on Table 3-5.
H. Replace the top cover.
3-l
Maintenance Model 1920
NOTE
Pin locations for the switches are shown on the decal on top of the RF
shield.
WARNING
All service information is intended for qualified electronic
maintenance personnel only.
3-3. INSTALLATION: (For use with Model 192)
A. Uisconnect the line power cord of the Model 192 and remove all test leads from its
input terminals for safety.
B. Remove two screws that hold the top cover to the rear panel and remove the cover.
C. Remove the top shield from the Analog Board by grasping it and FIRMLY lifting it off,
with a prying motion of the four retaining clips.
u. Carefully insert the connector of the 1920 into its mating receptacle on the Analog
Uoard. Take note of the orientation of the 1920 onto the 192 Analog Hoard as shown in
the figure below.
3-2
Maintenance
Model 1920
E. Connect the brown wire of the 1920 to P1014 on the Analog Board as shown in the figure
below. Connect the blue wire to PlOlG which is located on the ACV HI input terminal.
This is also shown in the figure below.
F. Replace the shield to the Analoy Board beiny careful not to pinch any wires when
engaying the shield into the retaining clips.
ti. Calibrate the lY20 per the procedure located on Table 3-4.
3-3
Maintenance Model 1920
3-4. PERFORMANCE VERIFICATION
3-5. Performance verification may be performed upon receipt of the instrument to ensure
that no damaye or misadjustment has occurred duriny transit.
NOTE
For instruments that are still under warranty (less than 12 months
since date of shipment), if the instrument's performance falls outside
specifications at any point, contact your Keithley representative or
the factory immediately.
3-6. RECOMMENDED TEST EQUIPMENT
3-7. Kecommended test equipment
performancefor verification is listed in Table 3-l.
Alternate test equipment may be used. However, if the accuracy of the alternate test
equipment is not at least 4 times better than the instrument specifications, additional
allowance must be made in the readinys obtained.
TABLE 3-l
Recommended Test Equipment For Performance Verification
ITEM UESCKIPTIUN SPECIFICATION MFK,
I
AC Calibrator O.lV, lV, lOV, 1oov H-P
+O.WzX
High Voltage Amplifier 1OOOV H-P 746A
(Used with Model 745A) +0.04%
UC Calibrator 1v +0.002x Flukl 343A
I
3-7. ENVIRONMENTAL CONDITIONS
3-8. All measurements should be made at an ambient temperature within the range of 18" to
28'C (GS" to 82'F), and a relative humidity of less than 8o'k.
3-9. PERFORMANCE VERIFICATION PROCEDURE
3-10. Use the following procedure to verify the basic accuracy for AC voltage in the
Model 191 or the Model 192.
3-4
Model 1920 Maintenance
WARNING
Performance verification should be performed by qualified personnel
using accurate and reliable test equipment.
3-11. INITIAL CONDITIONS
3-12. Before beginning the verification procedure, the instrument must meet the following
conditions:
A. If the instrument has been subject to extremes of temperature, allow sufficient time
for internal temperatures to reach environmental conditions specified (1X0-28'C).
Typically, it takes one hour to stabilize a unit that is 10