Keithley 147 User manual

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INSTRUCTION MANUAL
MODEL 147
NANOVOLT NULL DETECTOR
OCOPYRIGHT 1972, KEITHLEY INSTRUMENTS, INC.
PRINTED, APRIL 1977, CLEVELAND, OHIO, U. S. A.

CONTENTS MODEL 147
CONTENTS
Section Page
1. GENERALDESCRIPTZON---------------------------------------------- 1
2. OPERATION-------------------------------------------------------- 5
3. APPLICATIONS----------------------------------------------------- 21
4. C1I<CUIT DESCRIPTION----------------------------------------------
25
5. MhINTENANCE------------------------------------------------------ 31
6. REPLACEABLE PARTS------------------------------------------------ 51
SCHE~T~CS------------------------------------------------__-----__-- 65
0477 ii

MODEL 147
ILLUSTNATIONS
ILLUSTMTIONS
igure
NO. Title Pag:e
______-
i
la.
lb.
2.
a:
5.
6.
7.
a.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
FrontPanel.. ............................. 1
Front Panel with Cable ......................... 3
Front Panel Controls .......................... 4
Model 147 Rear Pmel Controls & Connections. .............. 6
Model 1481 Low-Thermal Input Cable ................... 10
Model 1483 Low-Thermal Connection Kit. ................. 10
Bus System for Model 147 ........................ 12
Thermal Sink Construction. ....................... 15
Normal Wave Form at Demodulator with Input Shorted ........... 17
Wave Form at Demodulator Shown with Some Pickup. ............ 17
Wave Form at Demodulator when Amplifier is Saturated .......... 17
8-cps Filter Circuit for Recorder Output ................ 18
Using Model 147 with 4-Terminal Connections. .............. 18
Exploded View for Rack Mounting .................... 19
Circuit UsingGuildline9144 with Model 147 Null Detector ........ 21
Circuit Using Guildline 4363DL with Model 147 Null Detector. ...... 22
Circuit Using Guildline 9120 with Model 147 Null Detector. ....... 22
Circuit Using Biddle 605001 with Model 147 Null Detector ........ 23
Circuit Using Leeds & Northrup 7556. .................. 23
Circuit Using Model 147 Null Detector with ES1 240, 8OOR and KS 925. .. 24
Block Diagram of Model 147 Amplifier Circuits. ............. 25
Model 1.47 Tnput Circuit. ........................ 26
Diagranl of Power Supplies & Battery Charging Circuit .......... 29
Model 147 Input Compartment. ...................... 32
Correct Wave Form in dc-to-dc Inverter ................. 36
Correct Wave Form in Oscillator Circuit. ................ 38
Improper Wave Forms in Oscillator Circuit. ............... 38
Correct Wave Form at Demodulator Test Jack ............... 41
Out-of-Phase Wave Form at Demodulator Test Jack. ............ 41
Top View of Model 147 Chassis ..................... 44
Bottom View of Model 1~47Chassis .................... 45
Transistor Locations on Printed Circuit 76 ............... 46
Capacitor & Diode Locations on Printed Circuit 76. ........... 46
Resistor Locations on Printed Circuit 76 , ............... 47
Resistor 6 Test Point Locations on Printed Circuit 76. ......... 47
Resistor b Test Point Locations on Printed Circuit 74, Bottom Face ... 48
Component Locations on Printed Circuit 74, Top Face. .......... 48
Resistor & Test Point Location on Printed Circuit 75 .......... 49
Capacitor & 'Transistor Locations on Printed Circuit 75 ......... 49
Resistor Locations on RANGE Switch (5102). ............... 50
Resistor Locations on RANGE Switch (S102). ............... 50
0477
iii

SPECIFICATIONS
SPECIFICATIONS
MODEL 147
iv
0477

MODEL 147 NULL DETECTOR GE:NLSALDESCRIPTIOX
SECTION 1. GENERAL DESCRIPTION
l-1. GENERAL.
a. The Keithley Model 147 is designed specificaLly RS a col,vcnicnt self-contained dc
electronic null detector. Its sensitivity is 0.6 x LOT3 microvolt per mi.llimrter or 0.03
x 10-e microampere per millimeter. Its resolution is better tllnn 3 nanovolts with a LO-oll:il
source resistance and 10 nanovolts with a 300-ohm source resistance. This corresponds Lo
a power sensitivity of 3 x lo-21 watt. Zero shift is less than 15 nanovolts for sourcf
resistance changes from 0 to 300 ohms. Line frequency r~!jcction is better than 5OOO:l 011
its most sensitive range.
b. The Model 147 has 16 ranges from 30 nanovolts full scale to 1.00 millivolts on a
zero-center meter. Meter accuracy is f2% of full scale on ~11 ranges.
c. For reliable and versatile use, the Null Detector is of solid-state design, cxccpi
for the first two input stages. It has high line isolation - lOl(J ohms - and battery
or ac power line operation.
FIGUPJ? La. Front ,>anel,.
0572 I

GENERALDESCRIPTION MODEL 147
l-2. FEATURFS,
a. Battery operation permits complete isolation from ac power lines, eliminating many
grounding problems. Battery operation also allows flexibility and convenience in use.
The Model 147 automatically recharges the battery if needed when the powercord is connected.
b. As an electronic null detector, the Model 147 is immune to mechanical vibrations.
It will also recover from a Z-volt overload on its inost sensitive range in less than 20
seconds.
c. Besides performing as a null detector, the Model 147 can also be used as a 2% direct-
reading nanovoltmeter.
d. The Null Detector has an output of ;tl volt at up to 1 milliampere for full-scale
meter deflections to drive a recorder or oscilloscope. Output accuracy is ;tl% of full
SCSlS.
e. A zero suppression circuit, furnishing up to 100 microvolts, permits measuring small
changes in a larger dc signal or compensating for thermal emf's.
l-3. APPLICATIONS. (Also see Section 3.)
a. The Model 147 is designed specifically as a null detector. It has sufficient sensi-
tivity to be used in most applications with all commercially available potentiometers, in-
cluding 6-dial models, ratio sets and resistance bridges, including Wenner, Wheatstone and
Kelvin Double Bridges. It can be used to make 4-terminal measurements.
b. Keithley's Model 147 is more sensitive than the finest galvanometer systems. It is
also immune to mechanical vibrations, thus eliminating the need for shock-free mountings.
Additional advantages over galvanometer systems'include the ability to recover from 2-volt
overloads in 20 seconds, much less off-null loading, plus considerably faster speed of
response.
0572

MODEL 147 CKNERAL DESCKIPTION
0572

GENERALDESCRIPTION MODEL 147
FIGURE 2. Front Panel Controls.
0572

MODEL 147 NULL DlXI:C'l'OR
SECTION 2. OPERATION
2-l. FRONT PANEL CONTROLS. (See Figure 2.)
a. AC CONNECTI?DLamp. l:hc Lamp is lit whcncvcr the unit is connected t0 i.lll xi. pwur
line and the POWERSUPPLY Switch is in tile AC or OFF position,
NOTE
b. BATTERY CHARGING Lamp. When lit, this Lanq indicates the ibattery ins clrnr:ini:. p1,:
charge current determines its brightness. If the lamp is noi l~it, tllc" LllC lbilCLtdl.\ ii
charged.
c. POGJIZRSUPPLY Switch. Ihe Switch controls tlrc mode of opcratiori for tile powel- suppI!:.
1. AC position: The Null Detector will opcratc from the nc power Lint. 'TIIC
battery will be charged if needed; then, the BATTEQY CIIARGINC Lamp will lil:ht.
2. OFF position: The Model 147 is not operating. Howcvcr , tlic battery wil~l lbc
charged, if nccdcd and if the power cord is connected.
3. BATI'ERY position: The Null Detector is operating from its battery. 'I‘liC ni'
power line is internally disconnected, whether or nut tile power cord is coluieclcd;
the AC CONNECTiXDLamp is off; the battery cannot be charged.
4. BATT. TEST position: When the POWERSUPPLY Switch is held in this posil:ioii,
the Model I.47 shows the state of the battery charge directly on its mctcr. Al I
circuits within the instrument are the same as for battery operation exccpl at Lllc
meter terminals.
POWERSUPPLY I Power Cord AC CONNKTED I BATTERY CIIARGINC La"{'
Switch Setting Connected Lamp (If battery is charging)
AC Yes 0” on
OFF YCS On Oil
NO Off Battery CllnnOt bc cli;lr::c!d
BATTERY Yes Off Battfry cannot IbC char;:ed
NO Off Battery cannot hc chnr~cd
Yes Off
BATT TEST Battery can,,ot bc cllar~:cd
NO Off LIattcry cannot be charged
TABLE 1. Indicating Lamps and POWERSUPPLY Switch Settings. The Table SllOWS tile
relationship between the front panel lamps, the power cord and the I'Oli'ER SUl'1~'I.Y
Switch setting.
0365

OPERATION MODEL 147 NULL DETECTOR
d. RANGESwitch. The RANGE Switch selects the full-scale meter sensitivity (either
microvolts or millivolts) for one of eight ranges, from 0.03 to 100.
e. FUNCTION Switch. The FUNCTION Switch selects the function - MICROVOLTS or HILLI-
VOLTS - which is to be measured.
f. ZERO SUPPRESSControls. Two controls determine
the amount of zero suppression.
1. The COARSEControl disconnects the suppression circuit (in OFF position) or
selects one of four suppression voltages in decade steps. Refer to Table 3.
2. The FINE Control is a continuously variable adjustment for the suppression
voltage set by the COARSEControl. It adjusts the range between the positive and
negative values of the maximum voltage set by the COARSEControl.
g. INPUT Receptacle. The INPUT Receptacle is of a special low-thermal design. Use
only the Models 14.81, 1482, 1486 and 1488 for mating connectors.
FIGURE 3. Model 147 Rear Panel Controls and
Connections. Circuit designations refer
to Replaceable Parts List and schematic diagrams.
2-2. RTtiR PANEL CONTROLSAND CONNECTIONS.
a. Line Voltage Switch. The screwdriver-operated slide switch sets the Model 147 for
117 or 234-volt ac power lines.
b. Fuse.
2. For 117-volt operation, use a 3 AG or MDL Slow-Blow l/@ampere fuse.
2.
For 234-volt operation, use only a MDL Slow-Blow l/16-ampere fuse.
c. Power Cord. The 3-wire power cord with the NEMA approved 3-prong plug provides a
ground connection for the cabinet. An adapter for operation from Z-terminal outlets is
provided.
6 0365

MODEL 1~47NULL DETCC'TOR
NOTE
A note above the power cord shows the ac power line i:rcqucncy for
which the rejection filter is ad.justcd. 'The instrument will work
at any line frequency from 50 t" 1000 cps, but ac rejection is bcsc
at the indicated frequency. Paragraph 2-18 dcscribcs adjustirl~; lilf
filter circuit.
d. DEMODULATORTEST Jack. A phone jack provides access to LllE denl"dLll~ator ior ti.5:
purposes.
f. OUTPUT. 'The OUTPUT Rcceptaclc provides
iL volt at one! mill.iampcrc f:or a iilll.-scale
meter deflection on any range.
f. GND and LO Tcrmiasls. 'The ground terminal. (GND) i.s conncctcd to tllc chassis ;~II)~!! 1)~.
third wire of the power cord. The low terminal is connected t" circui.t ground and cl!&:
low side of the input connection.
2-3. MODE01: OPERATION. The Model 147 operates cithfr irom an ac power line or irom iis
battery. b-or illost "SfS, it functions well from ac. Use battary operation, llo~ifver, i~1~
the ac power line will create ground loop or isolation problems. 1solnfi"n irun low to
ground is complete for battery operation when tllc power cord is disconnccl:cd; i,t is
greater than lOlo ohms wit11 the power cord connected. Al.so use battery operntiiln it>
reduce the 8-cps ripple which may appear at the output with i-11" input shorted in i&c
operation. See paragraph Z-16.
NOTE
Before using the battery operation, tll"r"ugllly read paragraph 2-4.
Improper battery "pcration can damage the battery pack and lead to
inaccurate measurements.
2-4. UXTERY OPERATION.
The Model 1.47 is supplied with a rcchargcablc h-volt,
ba:tery pack (Model 1489). 4 ampere-ilour Iliclr~l-~~l(llnilIr!l
Recommended: Do n"t usf the battery more tlliln cigirt COII-
secutive hours without recharging. At this discharge rate, the battery sl10u1d last abOUt
1000 recharge cycles.
NOTE
Permanent damage to the battery pack occurs if it is used for more
than 16 consecutive hours without recharging. At this discharge
rate, the recharge cycles are greatly reduced. Bflorf usi~ng tile
Model 147, check the state of the battery charge.
b. Cheek the battery charge before making a measurement. Hold the POWERSUPl'LY Switch
in the BATT. TEST position. The minimum acceptable charge is a meter indi.cntion oi ,8;
full. charge is shown by the BATTERY CHARGING Lamp not being lit. Recharge il needed.
Otherwise, battery operation is the same as for the ac power line operating mode; rcI:cr
to paragraph 2-5.
0365

OPERATION MODEL 147 NULL DETECTOR
When the battery is used beyond its capacity, two effects aye seen.
There is a shift in zero offset from ac to battery operation. Also,
the power supplies do not regulate and high ripple voltages appear
at the supply outputs. (See paragraph 5-8.)
c. To recharge the battery, connect the power cord to an ac power line. Turn the
POWERSUPPLY Switch to AC or OFF. The BATTERY CHARGING Lamp will light. The battery will
be charged only if needed, and the circuit automatically prevents it from being overcharged.
d. It is suggested that the battery be used during the day and be recharged at night.
Leave the instrument always connected to the ac power line; then turn the POWEKSUPPLY
Switch to OFF at night. After a fully charged battery is used for eight consecutive
hours ) it will recharge within 16 hours. Leaving the power cord connected has little
effect on the isolation: 1010 ohms with the POWERSUPPLY Switch in BATTERY position and
the shorting link between GND and LO Te?.minals disconnected.
2-5. OPERATING PROCEDURES,
a. Set the front panel controls as follows:
POWERSUPPLY Switch OFF
FUNCTION Switch MILLIVOLTS
RANGE Switch 100
ZERO SUPPRESSCOARSEControl OFF
NOTE
Make sure the ZERO SUPPRESSCOARSEControl if OFF. If it is not, a
suppression voltage is introduced, causing an error in measurements.
b. Connect the voltage swrce or null circuit to the INPUT Receptacle. Refer tO para-
graph 2-6 for suggestions.
c. Check the voltage shown on the rear panel Line Voltage Switch; connect the Model 147
to the ac pcwer line. Make sure the frequency shown above the power cord is the frequency
of the ac power line. At this point, the AC CONNECTEDLamp will light, asp will the
BATTERY CHARGING Lamp if the battery is being charged. If the circuit low is to be at
ground, put the shorting link between the LO and GND posts on the rear panel.
d. Turn the POWERSUPPLY Switch to the desired mode of operation, AC or BATTERY.
e. Increase the Model 147 sensitivity until the meter shows the greatest on-scale de-
flection.
1. Check the source resistance to make sure it is within the maximum value specified
for the range being used. (See Table 2.) If the maximum resistance for the more sen-
sitive ranges is exceeded, the Model 147 may not measure within its specifications.
2. Zero offsets seen when the Zero Suppress Controls are off will vary with the
quality of the circuit's thermal construction, See paragraph Z-14. When a Model 1488
Shorting Plug is connected to the Model 147 INPUT Receptacle, offset should be less
than 0.3 microvolt.
8 046613

OP1:llATION MODEL I,47 NULL I1lYl'ECTOR
1,, Make sure the signal is greater than Johnson noise in the source resistance (par-
agraph 2-12 ).
2. Use materials which generate a low thermal emL (paragraph 2-14).
3. Mini.mize temperature changes and thermal gradients (paragraph Z-14).
4 Reduce magnetically induced signals by proper shielding and minimizing experimen-
tal layout area (paragraph 2-15).
5. Eliminate ground loops through proper grounding and connection to the signal cir-
cuit (paragraph 2-16).
2-6. LOW-THEIMAL INPUT CONNECTIONS.
a Tlie easiest connection to the Model
14~7input is with the Model 1481 Low-Ther-
mal Input Cable, supplied with the instru-
mcnt Use tile Cable for temporary setups,
for measurements at several points, and
when fast connections are needed. The Mo-
del 148~1 connects directly to the INPUT
1~eceptacl.e.
b. Where more permanent setups are pos-
sible or where very Sow thermal connections FIGUKC 4. Model 1481 Low-Thermal Input
arc needed, use the Model 1482 Low-Thermal Cable. 'The Model 11+82 Low-Thermal Input
Input Cable. It is similar to the Model Cable is similar except it has bare copper
1481 , except it leas bare copper leads in- leads instead of alligator clips.
stead of nl,ligator clips. Clean the bare
wire! width a non-metallic abrasive, such as
Scotch Isrite, before making the connection. Making crimp connections, as possible with
illc> Model 1483 Kit, is best.
('. Si cadmium solder (Model 1503) is used for a connection, make sure the soldering
iron used is clean and that it has not been used with regular solder before. USC only
rosin solder flux. If possible, heat sink
all cadmium-soldered joints together to re-
duce generated thermal emf's. Careful
techniques will keep thermal emf's below
0.1 microvolt.
I'LCUIW 5. Model 1483 Low-Thermal Connecti
Kint . lieTcr to Section 6 for contents.
d. Use crimp connections with copper
wire and lugs for the best low-thermal
joints. Thermal emf's can be reduced to
10 nanovolts or less using the copper wire,
sleeves and Lugs found in the Model 1483
Low-Thermal Connection Kit. The Kit con-
tains a crimp tool, shielded cable, an as-
sortment of copper lugs, copper wire, cad-
mium solder and nylon bolts and nuts. It
is a complete kit for making very low ther-
mal measuring circuits. The Kit enables
the user 011 the Model 147 to maintain the
0466K

OPERATION MODEL 14,7 NULL DETECTOR
2-8.
FMATING OPERATION.
a. The Model 147 can be connected between two potentials, neither of which is at power
line ground. It can be floated up to ?4,00 volts off ground.
CAUTION
The front panel controls are electrically connected to the case. If the
power cord is unplugged, the case may be at a voltage equal
to the off-
ground voltage. use necessary e precautions.
-
b. For best results with floating operation, follow the steps below:
1. Remove the shorting link from the LO or GND Post on the rear panel.
2.
Connect the input circuit to the Null Detector. Operate as described in paragraph
2-5.
The zero suppress controls may also be used. Do not ground any recorders used
wfth this operation, since the low of the Model 14,7 output is no longer grounded.
3.
If power line frequency pickup is a problem, battery operation usually provides
better results.
2-9.
KECORDEROUTPUT. The Null Detector output for a full-scale meter deflection on any
range is $1 volt at 1 milliampere. Accuracy is ?I% of full scale. Output resistance is
less than 5 ohms within the amplifier pass band.. Output may be used during both ac and
battery operation. If the Model 147 is used for differential measurements, do not ground
the recorder connected to the output.
Model 147
P
Model 147 Model 147 Model 147
V
v b 4 P 4
LOW
1
FlGURF 6. Synchronized Buss System for Model 14,7. When two or m"re Null Detectors are
used in one system, an oscillator beat may occur; see paragraph 2-10. Synchronize the
instruments by connecting them as shown. See Figure 29 for point II.
12
04,67R

MODEL 1.47 NULL DETECTOR
2-10. USING MOIW THAN ONE MODEL 147 IN A SYSTEM.
a. The Model 1.47 oscillator is adjusted for a nominal freqnency ol 94 cps. ,,Oi.!i~VC~1~
slight variations in frcqucncy do occur between models. Wl,en using two or ,morc Xill I ill
tectors in one system, an oscillator beat may occur.
b. Synchronizing oscillators prevents an objectionable beat. Connect tllc! cwc in:,t iii-
"ents together at the collector of transistor (219 (Figure 29, Ipoint II), using iii: O.'i-
"icro.farad myl.ar capacitor.
c. At times the system is suc11 that the Null Detector lows may not bc conncctc~! di~-~~~t-
ly together. Then, use a 1:l transformer havi~ng a fairly higil impedance between tllc Cvil
instruments. A IlO-volt, low power isolation transformer works wit. USC n 0..5-:nicr<v
farad isolation capacitor in seri~es with iboth pri~mary and secondary wi~ndin~s o! C!IE i~~:i,i::-
former.
d. For several Null Detectors connected together, l,sc a synct,r"ni~zcil bliss :;ysli'T!, :iii
shown in Figure 6.
2-11. ACCURACYCONSIDERATIONS. For sensitive measurcmcnts - 10 mi~llivolts and bt~1lbi.x-
other considerations beside tile instrument affect accuracy. i:l:Ifcts not Iroticcnblc ,.i'!len
working with higher voltages are very important with mi~crovolt signals. Tl,c, ~lodel vi 7
reads only the signal received at its input; tllcrciorc, it is i~mportant tllat this signal
be properly transmitted from the source. The fol,i~owing paragraphs indi~cate iactor xiii c:.
affect accuracy: thermaI noise , input resistance, thermal emi's, shi~cldilll: iin<l (. il(.l.: *
connections. 'Table 4 also offers a quick rcfcrence to correct troubles wllich may occ11r.
1. The thermal noi~sc in any ideal resistance can bc dctarmi~ned Srom tiic Joi~nson !~rlis~'
equation: EZ",, = 4 I< T 11I; 1:q I
where Erms is the rms noise voltage developed across the voltage source;
T is tile temperature in degrees Kelvin;
R is the source resistance in ohms;
F is the ampl~ificr bandwidth in cps;
k is the Boltzmann constant (1.38 x 10e23 joules / OK).
yor an ideal resistance at room temperature (3OO*K), equation 1 simplilics to
Ii,", = 1.29 x lo-lo (RF)1'2 xi,
2. Peak-to-peak meter indi.cations are of "ore interest than tlrc rms vaiuc. i:xpcri -
mentally, the peak-to-peak Johnson noi.se is about live times the rms value. At r<10111
temperature, equation 2 becomes
EPP = 6.45 x 10-l' (RF)"' I:<,
where 13
PP is the peak-to-peak noise voltage developed across tile voltag" source.
0477