Keithley 164TT, 164 Service manual
INSTRUCTION MANUAL
MODELS 164,164TT
DIGITAL MULTIMETER
KEITHLEY INSTRUMENTS.
I N C.
CONTENTS
PRmTED OCT. 74
164. 164l-T
ILLUSTRATIONS
Figure Ii”. Title
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Front Panel
Front Panel Controls b Terminals, Model 164
Rear Panel Controls b Terminals, Model 164
Four-Terminal Resistance Measurements
Timing Diagram for AID COnVerfer
Typical Open-Collector outpue
Pill Designations For Printer output
Front & Rear Panels, Model 164TT
Multimeter Block Diagram
Analog Amplifier Block Diagram
A/D
Converter Block Diagram
Integrator Simplified Diagram
RANGE Knob Assembly
Chassis Assembly
servicing Of Chassis
PC Board I.ocacions
Side View of Chagsis
Chassis, Bottom
View
Calibration Controls
Calibration of Milliohm Current Source
Top Cover Assembly
Botfom cover Assembly
Component Layout, PC-254
Component Layout. PC-251
Component Layout, PC-248
cmlponent Layout, PC-255
Camponene Laywf, PC-250
Component Layout, PC-287
componenr Layout, PC-348
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SPECIFICATIONS
MODELS 164, 164TT
SPECIFICATIONS
I
iv
0)
0474
Sheet I of I
1275
KEITHLEY
To ensure the integrity of the chassis to earth ground connection only a Keithley
part number CO-7 line cord should be used for replacement.
is used ensure that the wiring polarity is the same as shown in the following dia-
gram.
NEMA
5-l5P
WHiTE WHiTE
INSTRUMENTS. INC
CAUTION
If a different line cord
Keithley Models to which
616, 6162, 702, 780
this warning applies: 160, 163,
164, 165, 171, 180, 190, 227,
MODELS 164, 164TT
SECTION 1. GENERAL INFORMATION
l-l.
GENERAL.
a. mm Mode. The Model 164 serves as a line aperated 3-l/2 digit multimeter having wide ranges for
measllrement of voltage, currerlt, and resiseance. I"
the D"M mode. the 164 offers seven dc volrage ranges
(from 1 microvolt per digit to 1000 volts). eight dc
current ranges (from 0.1 nanoampere per digif to 2
amperes), and eight resistance ranges (from 0.1 ohm
per digit LO 2000 megohms).
b. Milliobmmerer-Obmeter Mode. The Model 164
also Provides five additional resistance ra"ze8 for
mas";eme"fa requiring resolution to 10 microbm per
digit. Four-terminal measurement technique minimizes
the effects of lead and contact resistance in 1orresistance measurements.
C. Electronic High/Low Limit Trip option. The
Model 164TT provides independent electronic trip
CirCUitS for high and low limits. me trips are
"on-latching.
to= lamps, the Model 164TT offers rear panel r-elay contacts.
d. Di.sital Oue~ut Accessory. The Model 1602 is a
field-installable BCD output which my be used to interface the Model 164 wit31 a digital printer or computer.
I" addftio" to front pane1 indiG-
GENERAL 1NFORMATION
e. AC/DC Probe Accessory. The Model 1601 AC/DC
Probe permits ac voltage meas”reme”ts to 250
rms over a spa” of 45
Hz Co 45kHr. A probe mounted
volts
switch enables selection of ac or dc operation vichout disconnecting the probe.
1-2.
APPLICATIONS. The Model 164 is a general purpose instrument - used Fn Basic Research, Electronics
Development. and Process Control.
a. I" the Research Lab - When used vith a suitable
probe, transducer, or electronic circuit, Model 164
can be used for
digital indication of volts. amps.
or ohms. or through conversion, any physical parameter such aa temperature, pressure, and rpm.
b. I" Electronics oevelopmene Acriviry - "seable
for basic electrical m?as"reme"ta of voltage. current. or resistance.
@
0474
1
GENERAL INFOFwAT1ON
i
Control
MODELS 164. 164~~
TABLE l-1.
l+O"f Panel Controls and Terminals
Paragraph
RANGE SWITCH
In", "
"A, IIA. mA
n, krl, MO
Power
DMM
mn,n
SOURCE SWITCH
operate
Volt Limit
Sets the full range seneiei"ity and parameter to be measured (volts,
amperes, or ohms in the D"N made, or milliohms/obms in the Milliobm-
meter made).
Providea S.z"t?" voltage ranges from 1 mflli"olL full range to 1000 "OltS
full range.
Provides eight current ranges from 100 nanoampere full range to 1000
milliamperes full range.
Provides eight resistance ranges from 100 ohms full range to 1000 meg-
ohms full range.
Controls ac line power to insfrument
Sets instrument for DMM mode of operation
sets instrumenf for any one of five resistance ranges from 10 miniohm
full range to 100 ohms full range. (Milliobm current source terminals
m"st be connected to ""know".)
sets instrument for normal millioblmneter operation (non-voltage limit
made).
Sefs instrument for "elf-limit operation such that maximum open-circuit
voltage is limited to 20 millivolts. In this mode, measurement accuracy
is degraded depending on the resistance to be measured. see X-9.2.
Sets instrument for compensating thermal emfs in the milliobmmeter
mode. (Used in conjunction with the Zer" control.)
2-2b
2-b
2-k
2-9e
ZERO CONTROL
nn SO"RCE TERMINALS
I:
Red
Black
I!
Red
Black
I
Line Switch
AC Power Receptacle
1
zero Control
output Recepracle
BCD output Receptacle
Control Functional Description
(117-234V)
Permits adjustment of display zero.
currene source low (negative polarity)
Input high
Input law
Case ground
TABLE l-2.
Rear Panel Controls and Terminals
Sets instrument for either 117 or 234 volt lina power. 2-3a
Mates with 3-"tie ac line cord.
screwdriver adjusrmenr for zeroing o* 1 mv
Analog Output. (r 1 volt dc at full range at up to 1 milliampere).
Optional BCD output available with Model 1602 Digital Output Kit.
2-2d
*-la
Z-la
Paragraph
2-4b
2-3b
2-12
2-14 I
2 0774
MODELS 164, 164TT
GENERAL mFOF.MATlON
Jl203
MILL1
SOU
d204
ZERO
CONTROL
R505
OUTPUT
RECEPTACLE
5103
HI
JlOl J102
OMM INPUT
LO
FIGURE 2.
CASE SOURCE
5104 SWITCH
s1202 R1215
FronL Panel Controls h Terminals, Model 164.
ZERO
CONTROL SWITCH 51201
MODE/POWER
RANGE
SWITCH
SlOl
LINE
SWITCH
s202
AC POWER
RECEPTACLE
5201
I
0414
FIGURE 3. Rear Panel Controls b Terminals. Model 164.
3
SECTION 2.
OPERATING INSTRUCTIONS
1-l. 1NPUT CONNECTIONS.
a.
“inding Pose Terminals.
L. DMM Mode.
vided o” the front panel for connections EO input
HI (Red), input LO (Black), and chassis ground
(ccee”).
measurements, the source should be conneceed be-
tween the lower set of red and black termi”als.
Tile green rennin=1 may be connected to input LO
by use of a shorting link when grounded operation
is desired. see paragraph 2-11 for a discussion
Of fl”aZi”g operation.
‘. Xilliobmecer Mode. A separate pair of red
and black terminals is provided for use when making
four-rermina1 reSiSLa”ce nleaeurements.
ohm ct~rrent source provides a positive dc current
at ihe iHI (Red) terminal and is used in conjuncrio”
wietl ci,e DMM terminals.
discussion of milliohmeeer operation.
1641 Kelvin Test Lead Set (furnished with the Model
L64) simplifies connections co the resistance to be
measured.
tions for both voltage and current leads without
the need for separate cables.
b. Noise Considerations. The limit of resolution
in voltage and current measurements is derermined
largely hy rhe noise generated in the source. Stray
low-level noise is present in some form in nearly al1
electrical circuits. The instrument does not distinguish between stray and signal voltages since it measures the net voltage. When using the 1 mV and 10 mV
ranges, consider the presence of low-level elecrrical
phenomena such a~ thermocouples (thermoelectric effect,, flexing of coaxial cables (triboelectric effect), apparent residual charges on capacitors (dielectric absorption,, and battery actFan of two dFf-
ferenr contact materials (galvanic action).
1. Thermal Ems. Thermal ‘auf.9 (thermoelectric
porentiale) are generated by thermal differences
between two junctions of dissimilar metals. To
minimize ehe drift caused by thermal emfs, use cop-
per leads to connect ehe circuit to the i”s~rume”t.
The front or rear panel ZERO control cm, be used
to buck out thermal offsets if aecessary.
The KeiChley accessory Model 1483 Low Thermal Connection Kit confains a11 necessary materials for
making very low thermal cop,xr crimp connections
for minimizing thermal effecrs.
For voltmeter, ameter, and ohmmeter
Uinding post terminals are pro-
The rnilli-
See paragraph 2-9 for a
The Model
The Test Lead provides clip-o” connec-
NOTE
The inscrumen~ provides attenuation of line
frequency noise superimposed on an input
signal. The a-c rejection is specified as
f0110!.W:
WXR: Greater rha” 80 dB above one digit
for a voltage of line frequency or rwice
line frequency an the nw5t sensitive range?.
decreasing to 60 dB on the 100-millivolt
and higher ranges. 1000 volts peak-to-peak
mCXXim”m.
CMRR: Greater than 120 dB above one digit
at dc and 40 to 100 Hz ac.
100 volts peak-to-peak ac maximum
Proper shielding as described in paragraph 2-1,~
can minimize noise pick-up when rhe insrrumenc is
in the presence of excessive a-c Eiclds or when very
sensitive measurements are being made.
3. Magnetic Fields. ‘The presence Of strong mag“etic fields can be a potential source of a--c noise.
Magnetic flux lines which cut a conductor can produce large a-c noise especially at power line frequencies. The voltage induced due t” magnetic flux
is proportional to the area enclosed by the circuit
as well as the race of change of maflnetic flux. 2%”
effective wag co minimize magnetic pickup is LO ,’
=rra”ge all wiring SO Chaf fhe loop area enclosed
is as small as possible (such as twisting input leads).
h Second way t” minimize mnR”etic pickup is to use
shielding as described in paragraph 2-1,~.
C. Shielding.
Electric Fields. Shielding is usually “eces-
1.
say, when the instrument is in the presence of very
large a-c fields or when very sensitive measureme”ts
are being made. The shields of the measurement cir-
cuit and leads should be connected together t” ground
at only one point. This provides a “tree” configuration, which minimizes ground loops.
2. Magnetic Fields. Magnetic shielding is useful where very large magnetic fields are present.
Shielding. which is available in the form of plates,
foil or cables, ca” be used to shield the measuring
circuit, the lead wires, or the instrument itself.
500 volts dc,
2. A-C Electric Fields. The presence of electric fields
s”“rceB can have an effect on instrument operation.
A-C voltages which are very large with respect to
the full-scale range sensieivicy could drive the
a-c amplifier into saturafian, thus producing a”
err”“e”“s d-c oq.tpue.
4
generaced
by power lines or other
3. other Considerations.
a) Voltmeter Measurements. “se shielded in-
put leads when so”rcr resistances are greater
than lmegohm or when long input cables are used.
0414
MODELS 164, 164TT
b) current Measurements. on the InA CUrrent
ranges, no special shielding precautions need be
taken.
ed input leads are recormended.
put leads and =o”rce are recommended for m===“r=menes an the 10 megohm through 1000 megoh ranges
2-2. FRONT PANEL CONTROLS.
a.
tion of onerafine mode. The DMM oosirio” allows the
Model 164 co be used as a voltme&, ameter, and
ohmmeter. The mn and n positions allow the Model 164
to be used as a four-terminal resistance measuring
instrument.
power to the instrument.
b. Range Switch.
Of function and full range in the mm mode.
“rawever, on the UA and nA ranges, shield-
Power/Mode Switch. This switch permits selec-
The Power OFF pcxition disconnects line
This switch permits selection
3. Zero Posltia”. This position disconnects the
current source from the ““k”0w” for zeroing the
Model 164 in the milliohmeter mode only.
d. Zero Conerol.
,unction with the Source Switch (Zero Position) to
zero the reading in the milliohmeter mode. The co”rral may also br used in the DMM mode for adJustme”ts
on the 1 mV and 10 m” ranges.
adjusrmenr ie also provided for making co==== zero
=d,ustme”fs.) Place a short =cro== “oltm=t=r t=rminals before ad,usfi”g zero in Voltmeter mode.
This conrro1 is uSed in co”-
(A rear panel zero
2. “oltage Funcrio”.
Range Switch are designated in millivolts (mV) and
Volts (“) for full ranges from 1 millivolt to 1000
Volts.
inad”erranL Switching to the nanaampere ranges with
clockwise switch rOCatlo*.
sectors of the Range Switch are designated in ohms
(n), kilohms (K!?), and Megohms for full ranges
from 10” ohms to 1000 megohms.
fors of the Range Switch are designated in “a”“-
amperes (*), microamperes (NY), and milliamperes
(ma), for full ranges from 100 nanoamperes fO 1000
milliamperes.
C. Source Switch.
of operate, Volt Limit, or zero operation when using
rhe mR, n modes.
ma1 operation of the Model 164 as a four-terminal
resistance measuring instrument.
ope”-circ”it voltage of the mi11*otlm current source
to 20 millivolts.
racy is degraded depending 0” the resi=t=“C= to be
measured.
is connected (such as 10 0” the 1Q Range) the I”===urement accuracy is degraded by 5% since a 2On resistance is shunting the input.
A full stop at the 1000 Volt range prevents
Resistance Function. The resisrance (ohms)
3.
4.
Current Function. The current (amperes) s=c-
1. operate Position. This position permits *or-
2. Volt Limit Position.
POT example, if a full range resistance
The voltage sectors of the
This switch permits selection
This position limits the
ln this mode, measurement =CCU-
For maximum operaeor safety, connect the ground wire
of the line cord LO earth ground. This will ensure
that the CASE is at graund potential.
d. Funcfion,Ra”~e Selection. sehxr the PU”Cti0”
and Sensitivity using the RANGE switch.
OHMMETER mode, the RANGE switch is used in co”ju”c-
tion with the MODE Svirch as described in paragraph
2-9.
I” MILLI-
0774
5
---.-____I
I
“PERKrING INSTRUCTIONS
2-5. MODES OF OPERATION. The Model 164 permits measurements in either of two modes of operation, 1, Multfmeter ?lode (DMM) or 2) Ohmmeter-Milliobmmeter Mode (n,
mn).
a. Elulrimeter Mode (DMM . 1 I" the DMM mode, rbe
Model lb4 permifs measurement of uolrage, current,
and resiseance (LO 0.U per digit) for conventional
cAeas*relne*ts. To select the DMN mode, set the Mode
Switch to the DMM position.
Switch to the appropriate function and range.
b. Ohmmeter-Milliohmmeter Mode (0, mi2). I" either
thz1 or mil modes, the Model 164 permits mea~"=ement
Of resistance using a four-terminal voltage-current
method. To select the n or mii modes, set the Mode
Smirch to the desired "ohms" position.
rerminals ace provided for cu==ent and voltage se"sing. rhe Model 1641 Kelvin Test Lead Set ifurnish-
ed with the Model 164) simplifies connections to the
resiSta"ce to be measured.
as "m;2 SOURCE" provide a c"==ent in five decades
from 10 microamperes to 100 milliamperes, co==eg-
pending to positions on the Made Switch identi-
fied as IOK?, IOn, I!,, 100m0, o= 10mrt. The ter-
minals normally used for "MB measurements are for
voltage sensing when making four terminal resis-
tance meusurements. The Range Switch Of the Model
164 nl"Sf he set to rile lrn" function when using the
oirmmeter-milliohmmeter modes.
men set rhe Range
Separate
The terminals identified
HODELS 164, 164~
d. Innut resistance.
"f 10 m=whms 0" the 10 millivolt and higher =a"~*,
1 megohm on the l-millivolt range. FO= lomv and
higher =a"Ses, a 1000 ohm source eestatance will
introduce only 0.01% e==o=. 'ro maintain rated acw-i
racy o" the 1mV =a"~. the source reaiseance should
not exceed 100 ohms.
e. Off-Ground Measurements. The instrument low
terminal can be floated *500 volts above CASE ground
for voltage ,~~~%S"re?me"t~. Refer to paragraph 2-11
for complete instructions.
f.
AC Voltage Adapter Probe. The Model 1601 AC/DC
Probe permits convenient a-c voltage meaguremenfs from
0.1 volt to 250 volts rms o"e= a span of 4s HZ to 45
kkh. A probe-mounted switch provides convenient selection of,a-c o= d-c operation without disconnecring
the probe. Therefore, the probe may be pe=manently
attached.
2-7. aMMETER OPERATION (DMM Mode). This mode of
operation enables current meaS"=eme*ts from 0.1 "ano-
ampere per digit (100 nanoamperes full range) to 2
amperes with 100% overranging on all ranges.
a.
Range Selection. To select ammeter operarion,
set the Mode Switch to DMM, the" set the RanSe Switch
to the appropriate full range cu==e"t. As an ammeter,
the Model 164 provides eight ranges as given in Table
2-2.
The input haa a reeist="Ce
VOLTMETER OPERATION @MM Node). This mode of b.
2-6.
operation enables voltage meaS"=eme"eS from il microvolt per digit (1 millivolt full range) to tlOO0 volts.
Range Selection. To select "oltmeLe= operation
se:'the !Iode Switch t" DMM, then set the Range Switch
to the appropriate full range voltage. as a "olr-
meter, the Model 164 provides seven ranges as given
in Table 2-l.
TABLE z-1.
"olmeter operation
Range setcin Full P.a"Se Display Overrange Display
I El
from 300-volt overloads within five seconds on the
lm" range. "p CO 1000 volts peak may be applied
momentarily on any range without damaging the i"st=ument .
1 In”
10
In"
100
II"
1 "
10 v
100 "
"
1000
*Maximum allowable input is 1000 volts continuous inp"t on 1-"OlC to 1000~volt ranges. 1000 volts momentary, 300 volts co"rin"ous on lower ranges.
b. Measurement Accuracy. The voltage a~curac,. is
t(O.l% of reading + 1 digit) on all ranges.
C. Overload Recovery. The instrument will recover
1.000 In”
10.00 rn"
100.0 mv
1.000 "
10.00 v
100.0 v
1000. "
I
1.999
19.99
199.9
1.999
19.99
199.9
1000.
In"
rn"
in"
"
"
"
v*
Co""ecfio*s.
to place the Multimeter in series with the current to
be measured.
C. Measurement Accuracy. The current accuracy is
specified as '0.2% of reading, fl digit on all ranges:
Since the accuracy is specified ac the input terminals,
the loading effects should also be considered. See
Table 2-2 for values of shu"t resisfors.
d.
Off-Ground Measurements. The Model 164 low
terminal can be floated t500 volts above CASE ground
for current measu=eme"ts. Refer to paragraph 2-11
for complete instructions.
2-S. OWMMETER OPERATION @MM Mode). TXhis mode of
operaeion enables resistance meaS"=eme"eS from 0.1
ohm per digit (100 ohms full range) to 2000 megohms.
2,.
Range Selection.
@MM mode), set the Mode Switch to DMM, then set the
Range Switch to the appropriate full range resistance.
As an ohmmeter, the Model 164 provides eighr ranges
as given in Table 2-3.
b. Voltage Across the Unknown. "olfage drop is
100 millivolts at full range with 1.5 V max. into
a" open circuit.
known is determined by dividing the 100 millivolts
by the full range resistance.
c. Maximum Overload.
input tennina1s is 20 voles momentary and 1 Volt
co"ti""o"s.
d. Accuracy. As shown in Table 2-4.
Connect the input twminals so as
TO select ollmmeter operation
Thus the current through the "n-
Maximum voltage ac=oss the
(?
6
0474
UA
1
10
II.4
100
“A
ImA 1.000 mA
10 m.4 10.00 mA
100 m.4 100.0 mA
1000 mA 1000. m.4
1.000 LlA
10.00 pA
100.0 DA
TABLE 2-3.
ohmmeter operation
19.99
mA 1 0
199.9 InA
1999.
m.4 0.1 1
0.1 a
Range setting
100 n
1 !4
10 !4
100 kn
1 MST
10 Mn
100 MO
1000 Mn
Full Scale RanRe
Full Range Display
100 n
1 km
100.0 n
1.000 !4
10.00 kn
100.0 kn
1.000 MCI
10.00 MO
100.0 Mn
1000. Mrl
overrange Display
199.9 n
1.999 kl2
19.99 I&
199.9 kli
1.999 MO
19.99 km
199.9 Mn
i
.xXx
x.xX
xX.x
xxx.
1999. Mn
Impressed current
ImA
0.1 mA
0.01 mA
1 “A
0.1 )A
0.01 U.4
1 “A
0.1 n.4
Accuracy of Reading*
to.32 k 0.1 :i
20.3%
10.3%
$0.3%
!O
0474
.-
OPEP‘4TING 1NSTR”CTIONS
z-9.
OHMMETER-MILLIOIIMMETCR OPERATION ($2, “!i Mode).
I" the :r,mr moties, the Model 164 permits meaS"reme"t
Of resisrance from lOUS per digit to 2oon "Sing a
four-cermina1 voltage-current method.
d
summary of operation.
1. cannect OMM and ml2 source terminals to resis-
tance LO be measured.
2.
set RANGE ta h"
3.
set ?foLte Switch to desired range:
lOOmA, I::, 102, or 1000.
4. set source Switch to ZERO.
5. Adjust Zero Control for zero display.
6. Set Source Switch tc, OPERATE (except for "OLT-
LIMIT operation). Refer to section 2s9e for "OlC
Limit Operation.
b. cannectians.
provided for rile current source and voltmeter to faCiliCaLe four-terminal resistance measurements.
rermina1s identified as "n& SOURCE" provide a current
which may be selected in five decade steps from 10
microamperes to 100 milliamperes.
mally used for mm meaSureme"tS (lower pair) are the
"oltmeter terminals.
c. Range Selection. I" the mn,n mode, the current
supplied at the "Inn SOURCE" terminals (upper pair)
may be selected in five decade steps from 10 micro-
amperes co 100 milliamperes. when the Range switch
is ser to 1 In" sensitivity, the" the five positions
on ciie Mode svitch correspond to full ranges of 1cmn,
lOOna, 1.2, 1052, or 10057.
tance is determined by the current impressed at the
"l"G SO"RCE" terminals and the voltage sensitivity,
separate pairs of rermina1s are
me terminals nor-
since the full range resis-
l"lDil,
me
MODELS 164, 164'~
the displayed reading tlust be interpreted by calculating Ohm's law where R = V/r. we,, using the 1 m"
RP"c- setting, no calculation is necessary since the
Model 164 provides direct-reading ranges as marked
on the Mode SWiTCh.
used (other than 1 rn") the resistance must be determined by calculation since all decimal points will
be lighted (therefore the decimal p~int location will
be ambiguous). The direct-reading ranges available
on the Model 164 are shovn in gable 2-s.
d. Current Source. The current source in the
Node1 164 provides a constant current which may be
selected in five decade steps from 10 microamperes
to 100 milliamperes.
plia*ce "oltage up to 2 volts (in OPERATE mode only)
on au mnin mode settings. For example, the Model
164 may be used co furnish a currenf of 100 milliamperes to a load resisrance of.20 ohms (giving a 2
volt drop). I" the "OPERATE" mode, the Model 164
has an open-circuit voltage of approximately 15 volts
In the "VOLT LIMIT" mode, the Model 164 has an onen
circuit voltage of 20 millivolts.
If the resistance LO be measured is polarity
sensitive, the” care should be take” to connect the red (positive) terminal to the unknown so chat the desired polarity is obtain-
ed. (Conventional current flow is out Of the
red terminal and into the black terminal.)
If any other "Oltage range is
The source can provide a corn-
NOTE
r),
r
8
FIGURE 4.
MODEL 164
VOLTAGE LEADS Vl,VZ
CURRENT LEADS Cl, C2
RESISTANCE UNDER TEST
Four-Terminal Resistance Measurements
MODELS 164, 164TT
OPERATING INSTRUCTIONS
Full Ranges in mn and il Modes
Mode setting hange Setting* (wirh 100% overranping)
0
10 roil
100 mil
1 n
10 !I
100 11
1 m"*
1 Ill"*
1 In"*
1 mv*
1 In"*
*decimal location is valid only when lm" range is selected.
e. Voltage Limit Operation. The VOLT LIMIT mode
limits rhe own-circuit volraae across the m.G SOURCE
terminals to-20 millivolts. This feature is useful
when testing relays and switches to determine if a
"dry circuit" contact is present.
of "dry circuit" measurements, refer to ASTM Specifi-
l
cation 8539-70.)
MeaS”reme”LS performed in VOLT LIMIT InOde
NOTE
(For a discussion
should be used for approx. readi",qs &
since a portion of the mn Source current
is shunted through the limit resisror
(R1210, 1211, 1212, 1213, or 1214) as
shown on schematic 262420.
For “dry circuit:’ testing, set SOURCE switch to VOLT
LILlIT.
If an on-scale reading is indicated. the”
switch to OPERATE mode and record resistance of the
display. If an over-range condition is indicated then
a "dry circuit" open condition is present. since the
valcage is limited to 20 mV, the 164 canmt breakdown
the contact resistance unless switched CO OPERATE
care should be taken t" amid a transient
current pulse which may result from an overshoot of the SOURCE Switch when switching
from ZERO to VOLT LIMIT positions. When
making dry circuit measurements, the recommended procedure is to check the read-
ing in VOLT LIMIT mode, Lhen switch to ZERO
to adjust for zero offsets before taking a
reading in OPERATE.
The transient voltage which can be generated
I
by avershoor of the SOURCE Switch could be as
large as 15 volts. This voltage transient may
be sufficient to explode devices such as det"namrs and squibs if measured in the milli-
I
obmneter mode.
TABLE 2-5.
CAOTION
Max. Reading
mu source
19.99 mn
199.9 mn
1.999
19.99
199.9
!!
.i
'2
100 mA
10 ULA
lti
0.1 mA
0.01 ti
f. Power Dissipation in Unknown. The power dissipated in the unknown is a function of the current
impressed by the Model 164 current source. Power
developed. Worst-case, is dependent on the range selected and the compliance limit.
1. Volt Limit Mode. I” this mode, the compliance
voltage limit is set at 20 millivolts. The w"rst
case power dissipation would be a function of " x I
as shown in Table 2-6.
TABLE 2-6.
10
mn 20 In”
100
mn 20 m”
1
0 20 In"
10
n 20 m"
100
n 20 m"
2.
OPERATE “ode.
I” OPERATE mode, the power
2 InilliwattS
200 microwatts
20 microwatts
2 miCrowattS
0.2 microwatt
dissipation is a funcrion of range selected es
shown in Table 2-7.
g. Milliohmmeter Zero Adjpsc. set the source
Switch to ZERO. the Mode Switch to 10011 (or Lhe desired range), and the Range Switch t" 1 mV. Connecr
the unknown to the four terminals as described in
paragraph 2-9a.
Adjust the Milliohmeter Zero con-
trol to give a zero reading with a flashing r display.
I
.o
0414
9
OPmATING niSTR”CTIONS
“erS”S Currenf lneasurements are required. since the
mR currenf source in rhe Model 164 has a compliance
voltage range up to 2 volts, the Model 164 can be
used for material resting or semiconductor diode
checkout using the ranges given in Table 2-8.
V-I Characteristic Measurements
ode setting current Range setting Full Range.
10 mn 100 mA 1 rn" 10 mn
100 mn 10 "IA 1 "I" 100 mn
1 0 lti 1 In" 1 0.
10 n 0.1 n!A 1 El" 10 n
100 ii 0.01 mA 1 In" 100 0
10 mn 100 DA 10 mv* 100 mn*
100 ms2 10 * 10 Ill"* 1 n*
1 n ImA 10 mv* 10 n*
10 0 0.1 mA 10 mv* 100 **
100 n 0.01 In4 10 nlv* 1000 n*
100 nIlI 10 mA 100 "Iv* 10 n*
100 ;! 0.01 mA 100 "Iv* 10 kn*
100 mn 10 mA 1 v* 100 n*
100 P 0.01 m.4 1 v* 100 ki2"
-
10 Inn 100 mA 100 a"* 1 **
1 n 1mA 100 In"* 100 n*
10 n 0.1 mA 100 In"* 1000 n*
10 In<, 100 mA 1 v* 10 **
1 2 1mA 1 v* 1000 cl*
10 !I 0.1 nA 1 v* 10 k&l*
TABLE 2-8.
MODELS 164, 16433
NOTE
The maximum conc~nuous input voltage is
:lOOO volts an the 1000 volf xange.
1. when the Range Switch is placed in Ampere
positions 100 "A through 1000 mA, the MultimeLer
digit.31 display indicates the voltage across a
calibrated, self-contained resistor. The Range
Switch au~amatically selects the calibrated
ran
e resistor for current measurements from 1 x
7
lo-
to 1 ampere full range.
2. The Range Switch is designared in convenient engineering units, "A (nanoamperes), PA
(microamperes) and al.4 (milliamperes) with the
decimal point automatically positioned in the 3
display.
3. me full-scale current is determined by the
Range Switch.
range current ranges available on the Model 164.
Ampere Range
Refer to Table 2-9 for the full-
1 x 10-7
1.x 10-6
1 x 101;
1 x 1om3
1 x 10-2
1 x 10
1 x 10-l
I
t),;
4
,
*NOTE: Decimal point 1ocacion is not indicated when
the Range Swirch is set fo any posirion other than ~mv,
since all decimal points will be lighted. However,
decimal paint can be determined by a sample calculation
uf V : I for a given range.
2-10. DIGITAL DISPLAY OPERATION.
1. When the Range Switch is placed in voltage
positions 1 mv through 1000". the digital display
ind*caCes the actual voltage measured.
2. me Flange SWifCh is designated in convenienr
engineering units, rn" (millivolt*) and " ~"OlCS)
with the decimal point automacica11y positioned in
the display.
3. me full voltage range is determined by the
Range Switch.
4. A" overrange display up to a maximum of 1999
is provided by an overrange "I" Lndicator.
For an input greater than 1999, all digits will be
blanked except the overrange "1" indicator. The
polarity indicator will remain lighted indicating
the correct polarity. TO remo"e an overload condition, change the Range Switch to a lees sensitive
position or decrease the input signal magnitude.
C. ohmmeter Display.
1. When rhe Range Switch is placed in Ohms positions 100 n through 1000 MO, the Multimeter digital
display designates the valrage across the unknown
resistor with a fixed current applied.
2. The Range Switch is designated in convenient
engineering units, 0 (ohms), KO (kilohms) and M,i
(megohm) with the decimal point automatically
positioned in the readout.
3. The full-scale resistance is determined by
the Lange Switch. Refer to Table 2-10 for the full-
range resistance ranges available on the Model 164. ,
TABLE Z-10.
Resistance Display
1 x lo2
1 x 103
1 x 104
1 x 105
1 x 106
1 x 10'
1 x lo8
1 Y 109
01
/
i
4
0474
a. me low terminal can be floated above CASE
ground by removing the shorting link between the I.0
and CASE.
0
ground is greater than 100 megohms shunted by less
than 0.02 microfarad. Circuit ground may be floated
up to k500 volts with respect LO chassis ground in
the voltage and current modes.
b. When the inserument is used far off-ground
voltage or current measurements, rhe low terminal is
at floating potential. The instrument case ground
should be connected to earth ground through the line
and ground terminal.
and CASE must be disconnected.
1salatian from circuit ground to chassis
The shorting link between LO
OPERATING INSTR”CTIONS
h. Set the Range Switch to Amperes positions 1000
mA to 100 "ii while checking the readout so that *era
is indicated 0" all ranges.
i. RemoVe the Short circuit at the input terminals
1. Volts Ranges. me in?.trument will normally
read off zero a small nmount o" the 1 m" through
100 In" ranges because Of sensitivity co random
noise.
ranges 1" through 1000".
a readout overload where all digits except a "1" in
the overrange position are blanked.
indicate a zero readout, except for noise fluctuations.
The readout should remain at zero on the
2.
Ohms Ranges. All Ohms ranges should indicate
3. Amperes Ranges. All current ranges should
4
2-12. ANALOG OUTPUT.
output of 21 volt (non-inverting) at up to 1 milliampere for recording purposes.
ation, the analag 21 volt OUTPUT should not be connected unless a" external recorder is capable of
floating at !500 volts with greater than 100 megohms
iSOl&iO".
2-13. ZERO AD.J”STmNTS.
Short Lhe input terminals with a 10” terminal
a.
connection - preferably a short copper wire or clip
me instrumenr has an analog
For off-ground oper-
range.
C.
set the front pane1 zero control (P.1215) to
the full clockwise position.
If the digital display does not indicate +11
d.
to +13 mv, use the rear panel ZERO Control to adjust
the instrumenr.
e. Readjust front panel zero. zero is indicated
by flashing t polarity lights.
f. Check for zero reading on all ranges fro" 10 In"
to 1000 ".
NOTE
If there is an off zero reading on the 1 volr
range, it "ill be necessary to adjust CT‘? cmRENT OFFSET ADJ. 0" the underside of the chassis.
Refer to Figure 18.
g. set the Range Switch to ohms positions 1000 m
to 100 n while checking the readout so that zero is
indicated 0" all ranges.
j. After the preceding checkout is made, the instrument should be useable for a11 measurements WiCh
no further adjustments necessary.
2-14.
DIGITAl. OUTPUTS AND EXTERNAL CONTROLS.
a. General.
1. The Model 1602 Oigiral Output Kit provides
opriona1 BCO OUtputS and controls.
Included is a 50-pin PRINTEK/CONTROL Connector
2.
(receptacle) for mounting an the instrument rear
panel.
An output buffer card plugs into a prewired
3.
connector on the chassis for either factory or user
installation.
connecting card.
b. OUtpUt Codes and Levels.
The PRINTER/CONTROL 0"fp"tS are Binary Coded
1.
oechl (~0) ~lgnals with I-2-4-8 standard code.
me standard signal levels are as follows:
2.
output l.Qgic "1"
output Logic "0"
3. me Buffer stages uti1i7.e "Open Collector"
O"Lp"t transistors.
Buffer card replaces PC-255 inter-
see Table 2-11 (pg. 12)
see Table 2-11 (pg. 12)
NOTE
If clip leads are used on the input terminals,
the lead resistance may be indicated on the
100 n range since the last digit sensitivity
is 0.1 n per digit.
0474
c. OUtpUt Information.
11
OPERATING INSTRUCTlONS
TABLE 2-l'.
Model 1602 Outputs
rJICITAL OUTPUT: Em (1, 2, 4, 8) open collector
logic (Motorola MC 858P) represents each of 3
digits, averrange digit, overload ("I"), polar-
ity (+ = "1"). and decimal position (2 bits).
TIMING 0"TPUTS:
Clock:
rate).
count Interval: Logic "0" appears during count
interval (i.e. pulse width is proportional to Strobe: Open circuit to ground inhibits all outanalog inpur signal). put lines from conducting (closure to ground enFlag: Logic "1" appears for a 300 millisecond ables conduction).
interval out of a ~onversio" time of 500 milli- Hold: Closure to ground retains result of last
seconds. No change in buffer storage is made conversion in both the output register and the
outside this interval. display.
~"ternal clock pulses (10 kHz count
OUTPUT LOGIC LEVELS:
output Logic "1": open transistor collector to
ground with less than 100 microamperes leakage.
+6 volts maximum allowable applied voltage.
Ouf~uf Logic "0": transistor switch closure to
ground with less than 0.5 volt saturation voltage. +3s milliamperes maximum allowable current.
REMOTE CONTROLS:
MODELS 164, 164TT
i
i
INPUT
INTEGRATOR
ZERO
CROSSING
DETECTOR
BUFFER
STORE
PULSE
COUNT INTERVAL
I INTEGRATE - COUNT d ZERO-+/
n
FLAG
+ZOOmSA 200mS+lOOmS4
PICURE 5. Timi”! Diagram for A/D Converter.
---.
MODELS 164, 164TT OPERATING INSTR"CTIONS
~
Model 1602 PRINTER/CONTROL Connector Pi" Identification
Pin No.
1 1 x 100
2 2 x
3 4 Y
4 8 x Data 29 10 kHZ Cl‘Xk
_--______---______--------------------------------.------------------------------------~------
* 1 Y 101
6 2 x 101
7 4 x
8 8 x Data 33 Blank ---
9 1 x 102 Data 34 Bh"k
10 2 x lo2 Data 35 Blank _-_
11 4 x lo2 Data 36 Blank ___
12 8 x lo2 Ilate 37 Blank
13 1 x lo3 Data 38 Bh"k
14
15 1 x 10 6 Decimal Point 40 Blank _-_
16 2 x 100 Decimal Point 41 Blank _-17 Blank 42 Blank _--
18 Logic "1" Overload 43 Blank --_
19 Blank 44
20 count Interval see Table 2-11. 45 Blank
21 Blank
22 Blank
23
24 CO*O"
25 COINTIO"
ouepuc Function
loo
100
loo
lo1
101
+ = Lo ic "1" Polarity 39 Blank
Flag
Data 26 COGZIIO"
Data 27 COU!lllO"
Data 28 Blank ---
Data 30 Blank
D.Sfa 31 Blank
rat.3 32 Blank ---
See Table Z-11.
TABLE 2-12.
-__
---
--_
Pi" NO. Output Function
__---____----____-______________________-~~-
46 Blank
47 Hold
48 Blank
49 SLrObe
50 Blank
see Table 2-11.
see Table z-11.
_--
--_
FIGURE 6. Typical Open-Collector Output.
FIGURE 7. Pi” Designation For Printer output.
13
OPERATING INSTRUCTIONS
MODELS 164, 164TT
z-15. TRIP OPERATION (Model 164K1. The Model 164TT
is identical to the standard Model 164 except for the
"dditio" of high and law limit "on-latching trip circuits.
a. mip mimics. The Model 164TT has two independenely adjustable trips: one high limit and one low
limit type, non-latching.
b. Trip Levels. -200% to fZOO% of full range for
each trip.
set co trip at a display reading of f1000, the Model
164
would indicate a "Trip" level whenever the display exceeded +I~000 regardless of the function or
decimal puinr location.
C. Trip Setting. The Model 164TT provides front
pa"el screwdriver adjusrments for the high and low
trip circuits.
1. HI Trip. The front panel trip indicator lamp
serves as a "I level trip indicator and a momentar" contact p"shb"tto". when the button is depressed, the Model 164TT will display the trip
reference setting.
polarity and reference level setfing of the trip
circuit. A small chisel blade screwdriver is "eeded to make the adjustment.
2. LO Trip. The front ,mnel indicator lamp serves 3. contap Ratings. 10 volt-amperes, 0.5 ampere,
as a LO level trip indicator and a mmenrary con- 120 volts rms ac maximum. 6 watts, 0.5 ampere, 12
tact pushbutton. When the button is depressed,
For example, if the high trip level were
The display indicates borh the
the Model 164 will display ehe trip reference setting. The display indicates both the polarity and
reference level setting pi the trip circuit. A
small chisel blade screwdriver is needed ea make
the adjustment.
3. Set Precision. The Model 164TT will indicate
a trip condition when the reading is within a mlerance ?O.l% of full range with respect to the reference setting. Repeatability is fO.l% of full
range. Reference stability is iO.1% of full range,
"C.
4. Hysteresis. me trip circuit has a hysteresit
of less than 0.6% of full range. For example, once
the trip circuit is "tripped" the input signal must
vary by at least 0.6% of full range before the trip
can reset.
d. Trip Indication.
1. HI and LO Indicators. The Model 164TT provides visual indication of eriP point via front
panel indicator lamps.
2. Trip Contacts. One set of form A mntacfs
are furnished for each trip. Rear panel terminals
are provided.
"olts dc maximum.
a
SECTION 3. THEORY OF OPERATION
a. DMM Mode.
ot two sections packaged together in one chassis: 11
analog amplifier 2) analog to digital converter. me
analog amplifier utilizes a modulator/demodulator technique to achieve high dc stability. me analog-todigital converter is a dual-slope converter with two
readings/second conversion rate.
The basic digital voltmeter consises
1.
Input Resistor Divider.
attenuated by a divider network for FU\NGE Switch
IV, 10". 100" and iOOOV full-range positions.
2. Filter Network.
filtering of Normal Mode noise.
3. Modulator Circuit.
law level d-c input to an a-c signal.
The filter network provides
The i"P"L signal is
This circuit converls Lk
b. Milliohmmeter Node.
includes a currene source which provides current in
decade steps from 10 microamperes to 100 milliamperes.
.
Two addiLianal terminals are provided on the front
pane1 to permit four-terminal resistance meaS"renle"tS.
The voltmeter circuitry of the basic instrument is
used to monitor the voltage drop across the "MM Cerminals.
3-L. ANALOC AHPLIFIER OPERATION. A simplified black
diagram of the analog amplifier is shown in Figure lo.
a. voltage Amplifier Operation. The amplifier has
a full-ranee sensitivitv which is selected from 1
millivolt to 100 millivolts. *hove 100 millivolts,
the input signal is divided down to the 100 m" fullscale level.
as fallows: An input signal applied at the Input
High terminal is aetenuaced by a resistor divider,
The signal is filtered and applied to a modulator circuit
h final variable gain d-c amplifier provides a d-c
signal for the Analog out,x,t and A-to-D converter.
'rhe output is fedback to provide overall gain stability.
The a-c signal is then applied and demodulared.
The signal flow path can be described
The milliohqneter circuitry
7. Chopper Drive circuit. 'This circuit generaces
the drive voltage for the mod-demod cho,,pers.
C. OhmmeCer operation (Omltl. me illStr”ne”L
provides a known constant current which is applied
to the unknown resiseance. The voltage output is
proportional eo the resistance measured.
--..--
-
MODELS 164, 164~~
- ATTEN - FILTER -
Zero Mjustment Circuit. This circuit pro-
8.
vides limited adjustment of zero offset.
composed of potentiometer R505 and resistors 8503,
R504, R506, R508, and R509
and R1215, RI216 (see schematic 26242D).
0’
C. Ammeter Circuit (DKM Made). The instrument
utilizes the chopper amplifier described above with
various Range d&It resistors Rll6 through Pa*.
The chopper amplifier functions as a voltage ampli-
fier to provide an analog recorder output and drive
for the *-to-D converter.
TABLE 3-1.
d. clhmmerer circuit (DMM Mode). The i”strume”t
provides a constant--current using a voltage reference amplifier and series resistor R. The reference
voLtage E limits the open-circuit voltage to 1.5
volts maximum. The voltage reference is composed of
integrated circuit QA704 and reference diode 0702.
l e.
9
f$
to
Milliohm source.
1. AC voltage from T1201 is rectified by bridge
01201, filtered and supplied to the pre-regulator
QA1201. This is a three-terminal 15 volt regula-
tor. me 15 volt O”tp”f is connected through the
series pass transistor 41201 to the Hi terminal of
the rnll source, 31204.
The pass transistor is controlled by the op-
2.
ertional amplifier Q.41202. One input to QA1202 is
+10 voles (referred to power supply con!mon). This
is obtained from LWO zener diodes, 01202 and 01203
and a divider network R1202, R1203, and RlZO4.
R1203 is a potentiomeLer to permit compensation for
the tolerance of the zener diodes and the offset
voltage of QAlZOZ.
drop across the selected current sensing resistor,
one Of R1205 ehrou’gh R1209, which is in series with
the LO terminal, 51203.
3. When the current regulator is in balance, the
drop acroSS the current sensing resistor is qua1
eo the reference valtage and the current delivered
by the rnli source terminals is the proper value.
4. 1f the current source has no load, the volt-
age aCrOSS the terminals will approach 15 vo1rs.
when testing switches or relay contacts for “dry
circuit” applications, the voltage must be limited
to mm” or less. This is done by setting s1202 in
the Volt Limit position. The O”tp”c current is
then divided between the had and one of the volt
limit resistors, R1210 through R1214. Even with
open-circuited load, the volrage at the source terminals will not exceed 2Om”.
(See schematic 262420)
The other input is the voltage
(See schematic 26244E)
It is
3-4.
ANALOG-TO-DIGITAL CONVERTER OPERATION
a.
Ge”eC.d.
a dual-slope technique which has inherent line-frequency noise rejection. The analog signal is applied
to the integrator for 200 milliseconds which ia an
even multiple of the line frequency of 50 or 60 HZ.
The analog signal is then removed fram the integrator
input. The voltage on the integrator is then driven
to zero to complete the “olcage-to-time CO”“ersio”.
The time interval LD reach a “zero crossing” is
counted and displayed on the “Digital Readout” in
proportion to the original analog signal.
sequence is repeated, the integrator is rezeroed.
b.
The A-to-D Converter is composed of eight major
circuits as follows:
1. Oscillator or Clock
2.
BCD counter
3.
Program/Decoder
4. Integrator
5. zero crossing DeLector
6.
Buffer/Storage Register
7. Decoder/Dri”er
8.
Numerical Readout.
C. Oscillator or Clock. The Oscillator produces
pulses at a rate of 10 kilohertz far either 50 or 60
HZ operation.
BCD Counter. The BCD bunter COU”LS the Clock
d.
pulses with a total range of 5000 counts.
counter is composed of 4 individual counters designated 1, 10, 100, and 1000.
1. The “l”, “lO”, and “100” counters have a
capacity of ten CoUntS each.
2. ‘rhe “1000” counter has a capaciry of five
CO”ntS.
e. Pro.qram/Decoder. The Pro~ram,Decoder circuir
produces event cownands co conrrol the overall sequence of e”e”eS for a complete A-to-D conversions.
I
f. Infesxrator. The Integrator circuit operation
is composed of rhree periods.
1.
Zero Period.
tar amplifier is zeroed by a feedback rez.eroi?i:
circuit as shown in Fi&~re 12.
Sd are open to prevent integrator charging.
2.
Integration Period.
switches Sb, S,, and Sd are open.
closed to permit charging by the analog voltage
for an even multiple of the line frequency.
The analog-co-dfgical converter uses
2
3.4
0.1
‘TABLE 3-2.
Function
ZERO
INTEGRATE
COUNT
During this period the integra-
Switches Sa, Sb,
During this period,
Switch S, is
summary of Event Commands
Colmn.s”d
Before the
The
i
0474
17
FIGURE 11. AID converter Block Diagram.
I
18
0474
I- ~.
,- ----- .-.. -
-I_.
3. Discharge Period. During this period, witch
S, is open to prevent further charging by the analog signal.
drive the Integrator voltage t” zero. A reference
current of opposite polarity t” the input current
is applied through either switch SC or Sd. ‘The
Discharge Period ends when the Zero Crossing Deiec-
tar circuit detects a zero Integrator output.
8. Zero Crossing Detector. The Zero Crossing Detector circuit oravides a “Hieh” or “Low” level output depending on the polarity of the detected input.
Refer to Table 3-3 for a description of voltage ““tputs of the Zero Crossing Detector.
Buffer/Storageister. The Buffer/Storage
h.
Register is composed of “flip-flops” arranged t”
copy the states of the various BCD cou”fers. The
Buffer/Storage Register requires a Buffer St”re corn-
man* before any information ca” be transferred.
The “flip-flop” circuits provide coded information
for Decoder/Drdver and BCD outputs.
Decoder/Driver.
i.
decodes the BCD informatia” from the Storage Register into ten-line decimal code. The Driver circuit
then drives the proper numeral in each of the Num-
Either switch S, or Sd is closed to
The Decoder/Driver circuit
erical Readout tubes.
l j. Numerical Readout.
sists of four numerical indicarors and one oolaritv
indicator drive” by the Decoder/Driver, Pol&ity and
Overload Drivers.
The Numerical Readout con-
k. Summary of Operation. The operation of the
A-Co-D Converter can be described bv considerinr
a zypical conversion cycle. The Cl&k provides..
pulses at a rate of 10 kilohertz.
serves as a master timing control for rhe A-to-D
conversion cycle.
the “1000” counter which has five coded states,
namely 0, 1, 2, 3, and 4.
controls the sequency of commands based on the
coded states from the BCD Co”“Ler.
commands are described as shown in ‘Table 3-2.
“2” command initiates the integrator ZERO period
which removes any residual charge on the incegratar capacitor.
INTEGRATE period which permits a” integration of
the analog signal. At the end of the INTFGRATE
period, the “0.1” command initiates the COUNT period
When the “3,4” command is give”, the integrator is
charged by the analog signal for a period of 200
milliseconds.
the analog signal is removed and the integrator
‘JUtpUt is driven co zer” by a reference current.
The Zero Crossing Detector senses a zero crossing
of the Integrator output and removes the reference current.
show” in Table ,-3.
vided for control of ihe 1nregraror and Palarity
Storage Register. A pulse command is also produced to iniriate a Buffer/Stare.
Score command is give”, the Uufferlstorage Regiarer
copies the *CD Counter states at that lnstan~ of
time.
is the” avail.6l.e for the Decoder/Driver and external printout. The Decoder/Driver decodes the
Buffer/Storage output and drives the Numerical
Readour for a digital display. The conversion.
cycle is completed when the BCD Counter reaches
2000 counts and the PragramlDecoder provides a
“2” command to initiate a new conversion cycle.
The BCD coded infarmario” in the Register
The Liming is accamplished by
‘The Program/Decoder
The “3.4” command initiates rhe
When the “0,l” command is give”.
The Detector provides outputs as
The Cl.5 “OlC levels are pro-
‘The BCD Counter
‘The decoded
The
When the “uifer,
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