Z-l. Operating Instructions for the rlcdel 1920 installed in the ilodel 191 are as
follows:
2-2.
to 1000v.
voltage.
2-3.
Ilith the ilodel 1920 option, the ilcdel 191
The instrument displays the True Koot llean Square (TKilS) value of an AC
It has a frequency response of 20Hz to 100ktlz.
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
reads AC voltages froln 10 r;licrovolts/digit
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,
Select the desired range from the 4 ranges available.
8.
ati depress the ACV pushbutton.
The decimal point is positioned
by the range pushbutton.
Ensure that the I0JLL pushbutton is out (light off) unless measurements are to be made
C.
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.
Connect the signal to be measured between the INPUT HI ati LO binjiny posts. The
0.
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
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.
crest factor of three the displayed reading must be less than 100,000 counts (1V on
the 2V range).
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).
So long as the maximum input is not exceeded no damage will result in
CF
The figure illustrates that for a
Model 1920
I
0
Displayed Counts
Figure 2-l.
2-4. Operating Instructions for the Model lY20 installed in the Model 192 are as
follows:
2-5.
to 1ooov.
signal.
2-G.
input is 1OOOV Peak AC f DC; 2 x 107V.Hz. Use the Model
voltages as follows:
With the Model 1920 option, the Model
The instrument displays the True Koot Mean Square (TKMS) value of an AC voltage
The maximum reading is 199999.
Do not exceed maximum allowable input voltage. Instrument darnage may
occur.
Crest Factor VS. Displayed Counts
100000
192
reads AC voltages from 1 microvolt/digit
Overrange is indicated by OFLO. Maximum allowable
CAUTION
I
200000
192
to measure AC or AC + DC
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.
the ACV function. Pressiny the DC button while in AC t DC returns the
function.
Pressing the ACV button again will return the 192 to
192
the DCV
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.
CONNECT IllPUT to be measured between the HI HCV and LO bindiny posts.
E.
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).
crest factors exceediny that shown in Fiyure 2-1,
So long as the maximum input is not exceeded no damage will result in
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
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.
Maintenance
3-2. INSTALLATION: (For use with Model
A. Disconnect the line power cord of the Model
input terminals for safety.
B. Turn the DMM bottom side up and loosen the four screws in the bottom cover.
Hold the top and bottom cover together to prevent their separation and turn the DMM
C.
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
motherboard. Take note of the orientation of the
shown in the figure below. Connect the brown wire of the
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.
191)
1920
191
and remove all test leads from its
into its mating receptacle on the 191
1920
into the 191 motherboard as
1920
to Pin 7 of the DCV
Replace the top cover.
H.
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
Model 1920
Connect the brown wire of the 1920 to P1014 on the Analog Board as shown in the figure
E.
below.
Connect the blue wire to PlOlG which is located on the ACV HI input terminal.
This is also shown in the figure below.
Replace the shield to the Analoy Board beiny careful not to pinch any wires when
F.
engaying the shield into the retaining clips.
Calibrate the lY20 per the procedure located on Table 3-4.
ti.
Maintenance
3-3
Maintenance
3-4. PERFORMANCE VERIFICATION
Model
1920
3-5.
that no damaye or misadjustment has occurred duriny transit.
Performance verification may be performed upon receipt of the instrument to ensure
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 for performance verification is listed in Table 3-l.
Alternate test equipment may be used.
equipment is not at least 4 times better than the instrument specifications, additional
allowance must be made in the readinys obtained.
Recommended Test Equipment For Performance Verification
However, if the accuracy of the alternate test
TABLE 3-l
ITEM
3-7.
3-8.
28'C (GS" to 82'F), and a relative humidity of less than 8o'k.
3-9. PERFORMANCE VERIFICATION PROCEDURE
ENVIRONMENTAL CONDITIONS
All measurements should be made at an ambient temperature within the range of 18" to
3-10.
Model
191
UESCKIPTIUN
I
AC Calibrator
High Voltage Amplifier
(Used with Model 745A)
UC Calibrator
Use the following procedure to verify the basic accuracy for AC voltage in the
or the Model 192.
I
SPECIFICATION
O.lV, lV,
+O.WzX
1OOOV
+0.04%
1v +0.002x
lOV, 1oov
MFK,
H-P
H-P
Flukl
746A
343A
3-4
Model 1920
Performance verification should be performed by qualified personnel
using accurate and reliable test equipment.
3-11. INITIAL CONDITIONS
Maintenance
WARNING
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°C (1U'F) out of the
specified temperature range.
B. Turn on the instrument and allow it to warm up for two hours before using it with the
Model 192 and one hour before using it with the Model 1Yl.
WARNING
Some procedures require the use of high voltage. Take care to
prevent contact with live circuits which could cause electrical shock
resulting in injury or death.
3-5
Maintenance
Model 1920
Performance Verification
2V
2UV
zoov
7oov
2V
ZUV
zoov
2V
NV
2UUV
APPLIED INPUT
AT
1kHz
l.UUUOUV
1o.ouoov
lUO.UUUV
7oo.oov
AT ZUkHz
l.UUUUOV
lU.UUUUV
lUU.UUUV
AT 1UUkHz
l.UUUUUV
lU.UUUUV
lUU.UOUV
For 191
.9965UV to 1.0035UV
9.965OV to 10.035UV
T
99.65UV to 100.35UV
696.55V to 703.45V
.9935UV to l.UU65OV
9.Y35UV to lU.UG5UV
99.35UV to 100.65UV
.985UUV to 1.01500v
9.x5uuv to 10.1500v
Y8.5UOV to 101.5uuv
ALLUWAfJLf
:EAUIIVGS
For
192
.Y9G5UV to 1.0035OV
9.965OV to 10.035UV
99.GWV to lOU.35OV
696.55V to 703.45V
.9935OV to l.UU65UV
9.935011 to lU.UG5OV
99.35UV to lUU.65OV
.985UUV to 1.015uuv
9.85OUV to lU.15OOV
9x.5uuv to lU1.5OOV
7oov
ZUV
zov
ZV
2V
AT 3UkHz
700. oov
AT ZOHz
1o.uuuuv
AT 50Hz
10. ououv
AC + UC Mode
+1.uuouov UC
-1.uuuuuv UC
688.UOV to 712.oov
9.89UUV to 10.1100v
9.89UUV to 10.1100v
L
688.OOV to 712.OOV
Y.89OUV to 10.1100v
9.89UOV to 10.1100v
.995YUV to 1.ou41uv
-.9959uv to -1.uu410
3-6
Model 1920
Maintenance
3-13.
3-14.
instrument (191 or lY2). Calibration should be performed when any of the followiny
conditions occur:
3-15. RECOMMENDED TEST EQUIPMENT
3-16. Recommended test equipment for calibration is listed in the following table.
Alternate equipment may be used. However, the accuracy of the alternate equipment must be
at least 4 times better than the Model 1920 specifications,
listed in the Table below.
CALIBRATION
ITEM
This section contains information necessary to calibrate the Model 1920 in your
A. Annually
B. Installation of the 1920
C. Performance Verification indicates 1920 as out of specification
or equal to the specifications
TABLE 3-3
Recommended Test Equipment For Calibration
UESCRIPTION
SPECIFICATION MFK. MOUEL
-
A DC Calibrator
B
C High Voltage Amplifier
II
3-17. ENVIRONMENTAL CONDITIONS
3-18. Calibration should be performed under laboratory conditions having an ambient
temperature of 23
been subjected to temperatures outside of this range, or the higher humidity, allow two
hours minimum for the instrument to stabilize at the specified environmental conditions
before beginning the calibration procedure.
3-19. CALIBRATION PROCEDURE
3-20.
calibration cover.
the instrument to stabilize for two hours before performing the calibration.
AC Calibrator
(Used with Model 74SA)
Calibration Cover
_+l”C,
Remove the top cover of your instrument and replace it with the appropriate
and a relative humidity of less than 70%. If the instrument has
With the calibration cover in place allow the internal temperature of
+1v
r.uw'/
U.lV,
Hl.U22%
IUOUV H-P 746A
+0.04x
lV, lOV, 1uuv
--
Fluke
H-P 745A
Keithley 1913 (191)
343A
3-7
Maintenance
Model 1920
WARNING
Some procedures require the use of high voltage. Take care to prevent
contact with live circuits which could cause electrical shock
resulting in injury or death.
R406 C412
R42G
STEP
1
2
*AUJU
3
4
5
6
Model 1920 Calibration Adjustments
TABLE 3-4
Model 1920 Installed in the 192
Calibration Procedure
KANtiE
2
2
KNT: Adjust the UC calibrlator until the display reads 1.00000 +I0 digits.
leads and take note of the reading.
Keadiny is l.U04lJU, adjust K411 to read 1.00200).
?peat Steps and 2 until there is < 10 digits
FWCTIUN
ACV + KY
ACV + UCV
ACV
ACV
INepeat Steps 4 and 5 until they
APPLIEU INPUT
1.lllllloov UC
-1.UOUUUV UC
Adjust K411 to l/Z the difference (Example:
l.UlxlUUV AC
at SUUtir
.llJlJUlJV AC
AUJIJSTMENT
*Calibrator
*K411
I
change in reading from + to -.
K407
K4Z6
are within tolerance.
KEAUINti
I.UOOOO ?lO counts
l.UOOUU QO counts
I
1.00000 ?lO counts
.lOOOlJ i-10 collnts
Keverse th
3-8
Wodel
1920
c
I;iP
7
c, mu
Y I 2lJlJu
( 700V AC Max)
10 2UU
20
TABLE 3-4
Model 1920 Installed in the 192
Calibration Procedure (cont.)
FUNCTION APPLIED INPUl AUJUSTMENl
T
ACV
ACV
ACV
ACV
1o.oLwLlv HC
at SUUtir
lUU.UUUV AC
at 5UUtlr
5UU.UUV AC
IUU.UUUV AC
at
1Wktiz
Caution: Use
an insulated
aliynlnent tool
K4U0
K405
K404
C413
Maintenance
KEAUINti
5LlO.UU r10 counts
lOO.llU +25u counts
11
12
13
14
2
20
I
Kepeat Steps lU-12 until no chanye.
Kepeat Steps l-l:! to verify the readings.
tliyh frequency (100kHr) measurements are sensitive to component location.
Uo nut move or bend the components in the input area (C401, iKWJ, etc.)
Kecalibration is necessary if these components are moved.
1UUkHr cannot be brouytit into specification,
section.
Some procedures require the use of high voltage. Use an insulated alignment
tool.
electrical shock resulting in injury or death.
I
Take care to prevent contact with live circuits which could cause
/\cv
ACV
l.UUUUUV AC
at 1UUkHr
lU.UUUUV AC
at 1UUktir
I
NOTE
WARNING
c4u2
C4U7
refer to the troubleshootiny
l.OUOU *50 counts
lU.ULlUU ~100 counts
If the 1uuv
3-9
Maintenance
Model 1920
TABLE 3-5
Model 1920 Installed in the 191
Calibration Procedure
STEP
1
2 2 ACV
3 2 ACV
4 2 ACV .lUUUUV AC 11426
:, IRepeat Steps 3 dnd 4 until they are within specification.
ti
7 2uu ACV
8
9,
10
11 20 ACV lU.UUUUV AC c4u7
12 Hepeat Steps 9 thru 11 until no change.
KANtiE
2 ACV
20
zuuu
( 7UOb AC Max)
LOU
ii
FWCTIUI~
ACV
ACV
ACV
ACV
I\PPLIEU INPUT
1UUmV AC
at 50011r
1UmV AC
at SUUHr
l.UUUUUV AC
at SUUHZ
at 5UUHr
11).uouuv AC
at 5UUHz
IUU.UUUV AC
at SUUHZ
suu.ouv AC
lUU.UUUV AC
at 1lJUkHr
l.UUUUUV AC
at 1UUkHz
at 1OUkHr
AUJUSTMENT
K411 Minimum Reading
K411
K4U7 l.UUOUU *lo counts
K4UG
I<405
11404 5u0.00 +10 counts
c413
Caution: Use an
insulated alignment tool.
c4uil 1.0000 +50 counts
KEAUING
Minimum Reading
.lUUUU *lo counts
10.0000 *lo counts
100.000 ?lO counts
100.00 i25ll counts
10.0000 *loo counts
13 Kepeat Steps 1 thru 11 to verify the readings.
NOTE
Hiyh frequency (100kHz) measurements are sensitive to component location.
Do not move or bend the components in the input area (C401, K403, etc.)
Recalibration is necessary if these components are inoved.
1UUkHz cannot be bt-ouyht into specification,
section.
3-22.
3-23. The troubleshootiny instructions contained in this section are intended for
qualified personnel having a basic understanding of analog and digital electronic
principles and components used in precision electronic test equipment. Instructions have
been written to assist in isolating the defective circuit or subcircuit.
specific defective component has been left to the technician.
3-10
Troubleshooting
refer to the troubleshooting
If the 1OUV
Isolation of the
Model 1920
NOTE
For 1920's that are still under warranty (less than 12 months
since date of shipment), if the 1920's performance is outside
of specifications at any point,
or the factory before attempting troubleshootiny or repair.
3-24. Troubleshooting Procedure
3-25. Table lists step by step checks of the lnajor circuit blocks of the 1920. Follow
Table 3-G to locate the trouble.
Performance Verification of the Model 1920 is necessary if any of
the following occurs.
contact your Keithley representative
NOTE
Maintenance
1)
Kemoval /rep1 acement of 1920
2) Removal/replacement of shields on the 1920
WARNING
Some procedures require the use of High Voltage. Take care to prevent
contact with live circuits which could cause electrical shock resulting in
injury or death.
TABLE 3-6
Model 1920 Troubleshooting (cont.)
STEP
1
7
8
9
ITEWCOf1PONENT
J1006,
U401, Pin 7
U401, Pin 4
U403, Pin 8
(Brown wire 51008)
U401, Pin G
Q408, Pins 2
Q408, Pin 3
Pin 1
anJ. 5
Turn on Power. Select the
AC function ard 2V range.
t5V <lOOnV AC noise
t15V *lV DC <lOOnV AC noise
-15V +lV DC <lOOnV AC noise
Apply 1 volt at 1ktlZ
1 volt DC
1 Volt AC at IkHZ, no DC Offset
+3V to t8V DC, within
of each other
UV t 25mV
REQUIKEO CONDITIOll KEHAKKS
+5v supply
t15v supply
-15v supply
1920 output
u401 output
1OmV
Differential Output
of Q408
Input summifq junction
Maintenance
-
STEP
10
11
12
13
14
Model 1920 Troubleshooting (cont.)
ITEM/COMPONENT
TABLE 3-6
REQUIRED CONDITION
Select 2ov range
a,j apply 1OV AC at 1kHZ
Select 2oov ranye ard
apply 100 V AC at 1kHZ
Select 700V range ard
apply 350V AC at 1kHZ
Select AC + DC function
ard the 2V rarqe. Apply
1v DC
Select AC apply IV DC
Model 1920
KEIlAKKS
(virtual ground)
If display overranges
check (1406 an3 Q407
for gate drive ard
signal
If
display met-ranges
check Q404 ard Q405
for gate drive anl
signal
If display wet-ranges
check Q402 arrl Q403
for gate drive drd
signal
Check display for 1V
if not, check (1401 an3
K401
Oisplay approx. OV
if not, check Q401
K401, c401
NOTE
If the 1OOV 1OUkHz adjustment cannot be brought into specification,
check the spaciny between C4Ul and K403. If these components have
been bent toward or away from each other, C413 may not have adequate
calibration ranye.
1OOkHz response on all ranges.
Moviny C401 and K403 closer toyether increases the
Check and adjust, if necessary.
3-12
Model 1920
SECTION 4. MODEL 1920 THEORY OF OPERATION
4-l. The Model 1920 is a plug in AC(+UC) to RMS converter with variable yain. The gain
factor conditions the AC input voltaye for application to the A/U converter.
4-2. The input siynal is applied through GIN (0.05uF) and KIN (2Mrl) to 4408. For
AC+UC operation GIN is shorted by Relay K4Ul.
variable yain inverting type with gain from-U.001 to-l (see table below). The gain is
selected accordingly by the double FET switches Q402-Q407. Two FETs are used for each
range.
K41G to effectively attenuate high frequency (1UUkHz) signals.
They are configured in a T-type attenuator with the 1Uk resistors K413, K414 and
The two stage amplifier (op amp) is a
Theory of Operation
4-3.
Q408. 4408 allows the reduction of input bias current.
because an auto zero cycle is not possible on the AC or AC+UC functions. Any input bias
current will show up as an input offset voltage.
u401. The output of U4Ul is applied to the KMS converter U403. C409, C41U and K42U make
up the two pole filter that is located at the output of U403. The output of U403 is a UC
signal which is applied to the A/U converter.
auto zero A/D input by adjusting R426.
output offset.
The op amp is a two stage amplifier. The first stage is confiyured around dual FET
This reduction is necessary
The second stage is configured around
A small UC offset may be applied to the
This allows compensation for the KMS converter's
TABLE 4-l
Ranging Information
Ranye tiain
2v 1
2ov
2ouv
7UOV
l/10 (217k f"K4U6) 11 2M
l/100 (19.6k + K405)1) 2M
l/lOUU
UP Amp Feedback Resistance Engergized FETs
None
Q406, q4u7
Q404, Q405
(2.12k + K404)I)
(19.GK + R405)1/ 2M
Q402, Q403,
Q404, Q4U5
.I
4-1
-
Model 1920 Biock Diagram
FET
Orive
Range
-
Select
Model 1920
Repldieabl
e Parts
SECTION 5.
5-l.
5-2. This section contains information for ordering replacement parts. The replaceable
5-3.
5-4.
General
parts list is arranged in alphabetical order of the circuit designations of the
components.
given in Table 5-1.
Ordering Information
To place an order or to obtain information concerning replacement parts contact your
Keithley representative or the factory.
When ordering,
a. Instrument Model Number
Instrument Serial Number
b.
c. Part Uescription
Circuit Designation (if applicable)
d.
e. Keithley Part Number
A crass reference list of manufacturers containing their addresses is
include the following information:
REPLACEABLE PARTS
See the inside front cover for addresses.
5-5. Factory Service
5-6. If the instrument is to be returned to the factory for service, please complete the
Service Form which follows this section and return it with the instrument.
5-7. Schematic and Component Layout
5-B. The Schematic and Component Layout follow this section.