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HEWLETT
PACKARD
SERVICE INFORMATION FROM HEWLETT-PACKARD
2nd Quarter 1990
Operational Ampllifier Basics
Introduction The op amp is, therefore, an ideal Ideal Op Amps With Negative
building block for all kinds of analog Feedback
It can be mathematically shown that tasks. In practice, no single charac-
if an amplifier has: teristic listed above can be fully The most common op amp circuit con-
I an infinite high gain, achieved. The values that can be prac- figuration uses two external compo-
tically obtained are nevertheless such nents: 1) an input component and 2)
I an infinite bandwidth, that the resulting performance is a feedback component (see Figure 3).
I an infinite high input impedance, extremely useful. When the feedback component is be-
and tween the op amp output and the
I a zero output impedance, -input, the circuit is said to have
negative feedback. When the feed-
then its characteristics can be totally Op Amp Fundamentals
determined by external components
connected in feedback loops. Such an An op amp is a very high gain dc I
amplifier and usually has voltage V+
"ideal" operational amplifier (op Power Supply
amp) is shown in Figure 1. Since RIN gains in the range of 20,000 to
is infinite, there is no current flow into 1,000,000. The detailed schematic
symbol of an op amp is shown in n
1 Input " e ~ i n g ~
either input terminal and the differen-
tial input voltage is zero. If there is Figure 2a with the simplified symbol
an output voltage Eo present, it can shown in Figure 2b. Ioninverting output
Input
only be the result of an infinitesimal Power
voltage at the input. These are Supply
theoretical considerations only. As shown in Figure 2a, the -input
of the op amp is called the inverting Ground
input, and the +input is called the
noninverting input. If an input signal
is applied to the -input, with +input Fig. 2a. Detailed schematic.
grounded, the polarity of the output
signal will be opposite to that of the
input signal. If an input signal is
applied to the +input, with the -in-
put grounded, the polarity of the out-
put signal will be the same as that of 0
the input signal. For an ac signal, this
means that the output of the op amp
will be 180 degrees out of phase with Fig. 2b Simplified schematic.
a signal applied to the - input, but in
phase with a signal applied to the
Figure 1. "Ideal" Operational Amplifier finput. Figure 2. Op-amp schematic symbols
Pub. No. 5952-3458 Hewlett-Packard 1990
WWW.HPARCHIVE.COM
sum of the currents toward any point
in a network is zero) to the inverting-
input terminal of the op amp, it can
Feedback be seen that the input current must
IIN- Component be equal and opposite to the feedback
current. Extensive use will be made
of this important result:
IFB = -IIN
The Equivalent Circuit
1 I The schematic diagram of the op amp
with negative feedback may be
simplified, using the previous results,
to the equivalent circuit shown in
Figure 3. Op amp circuit with negative feedback
Figure 4.The equivalent circuit is ob-
tained by recalling that I,, is equal
back component is between the op amplifies the differential input vol- and opposite to I,, and so Figure 3
amp output and the +input, the cir- tage (VIN) producing an output vol- can be relabeled as shown in Figure 4.
cuit is said to have positive feedback. tage (E,) with a polarity opposite to
that of VIN. This output is fed back Since VI, is nearly zero, the inverting
In Figure 3, an op amp is shown with through the feedback component and input of the op amp can be considered
negative feedback. EIN is the inut sig- opposes the input voltage that pro- to be at ground potential. This
nal, VI, is the differential input to the duced it. simplifies the diagram of Figure 4 to
op amp, and Eo is the op amp output. the important equivalent circuit
The open loop gain is defined as the Because the negative feedback signal shown in Figure 5.
ratio of E, to VIN: opposes the input signal, VIN is very
small. Therefore, the higher the gain The equivalent circuit shown in
of the op amp, the smaller is VIN. In Figure 5 shows why op amps with
Open-Loop Gain =
EO
- fact, for some calculations, VIN can be negative feedback are so useful. The
assumed equal to zero and the invert- input circuit is electrically isolated
ing input at virtually the same poten- from the output circuit, yet the cur-
The closed-loop gain is defined as the tial as the noninverting input. rent flowing through the input com-
ratio of Eo to EIN:
The relationship between the input
current (IIN)and the feedback current 'If V, were actually equal to zero, the output
,
EO of the op amp would also be zero and the op
Closed-Loop Gain = - (IFB) is most important. Assuming
that VI, is equal to zero*, it follows amp would be useless. In reality, VI, is a very
small voltage (usually less than a millivolt).But,
from Ohm's law that no current can for the purpose of calculating input and feed-
The open-loop gain is the gain of the flow into the op amp. By applying back currents, very little error is introduced by
op amp and this gain is independent Kirchhoff's current law (the algebraic approximating V,, as equal to zero.
of the input and feedback compo-
nents. The closed-loop gain, how-
ever, depends only on the values of tlN ---b
the input and feedback components 1
when the closed-loop gain of the cir-
cuit is much less than the large open-
loop gain of the op amp. 'IN-
I I--
l------
Input
Input Current and Feedback Component
El,
Current
i
P
When an input signal (EIN) is applied
to the circuit of Figure 3, a current
(IIN) flows through the input compo-
nent and a voltage (VIN) develops
I r-
across the input terminals of the op
amp. The very high gain op amp Figure 4. Negative feedback op amp circuit with equivalent feedback current shown
2 BENCH BRIEFS 2ND QUARTER 1990
WWW.HPARCHIVE.COM
equal to the E,, source impedance for
balancing purposes of the differential
input stage.
Component Component
The Inverting Op Amp
EI, and E, are inverted as is indicated
by the negative sign for the gain (see
I
Figure 5. Equivalent circuit of Figure 4
Figure 10). R3may be included instead
of a ground connection of the nonin-
verting input only because of a less
than ideal amplifier (less than infinite
input impedance). R, should be equal
to R,, again for balancing purposes.
ponent dictates what current must Table 1. Table of Circuit Functions If the characteristics are close enough
flow through the feedback compo- Circuit Input
to ideal, then input B is at ground
nent. By choosing different input and Function :omponents level. By definition, input A must also
feedback components, different cir- be at ground level since there shall be
.
cuit functions can be performed. The 1 ..I.
Resistor no potential difference between in-
Resistor
circuit functions listed in Table 1 will Capacitor
puts A and B. Point A is called a vir-
be discussed later in this article. tual ground.
Figure 6. Simple voltage divider Figure 7. Simple voltage divider set at Figure 8. Simple voltage divider with op
50 percent amp providing isolation
Figures 6 and 7 illustrate a very simple feedback. An op amp connected in
concept in conjunction with an op this way is often referred to as a voltage
amp. The potentiometer P is used as follower or an impedance converter.
a variable voltage divider and the vol-
tage delivered to the load is in a linear An additional characteristic that is im-
ratio with the shaft rotation. This will portant for an op amp is stability. If
only be the case if the load is an infi- the input is zero, the output will also
nite resistance, or is very high in com- be zero. The op amp must be free of
parison to the resistance of P. As an drift or offset voltage.
example, if P and the load are each
10 kilohms and P is set at 50 percent,
the division ratio will not be 1/2 but The Noninverting Op Amp
2/5, as shown in Figure 7.
In the configuration shown in Figure
If an op amp is connected between 9, E,, and E, are in phase. The closed GAIN = 1 FOR R = 0 OR R, = co
,
the movable contact of P and the load loop gain is controlled by the ratio of R,, CO
as shown in Figure 8, the op amp will R, and R,. If R, = 0, then the amplifier
r
I, = 1, INDEPENDENT OF R2
provide perfect isolation. The op amp is simply a voltage follower and R,
must have a closed loop gain of one. becomes meaningless. However, in
This is possible with a 100 percent practical applications, it will be made Figure 9. Simple noninverting op amp
2ND QUARTER 1990 WWW.HPARCHIVE.COM BENCH BRIEFS 3
I
Figure 12. Simple differential operational
amplifier
Figure 10. Simple inverting operational
amplifier
Figure 11. Simple summing operational
amplifier
The Summing Op Amp small signals in the presence of 60 ity of EIN. If E,, is a symmetrical
Hertz noise. The 60 Hertz noise com- square wave, Eo will be a triangle
The summing op amp shown in mon to both inputs is rejected and the wave. For E,, = sin X the output is
Figure 11 is simply an inverting op op amp amplifies only the small signal -cos X. The output leads the ;nput
amp with multiple inputs. Since input
A is a virtual ground, there can be no
difference between the two inputs. by 90". "\
current flowing over A from one input Note that an ideal differential op amp
into another input. The total input produces neither a differential-mode
nor a common-mode output in re-
The Differentiator Op Amp
current is I, = I,. The number of
inputs is only limited by practical sponse to a common-mode interfer-
ence input.
As shown in Figure 14, Eo is propor-
considerations. tional to the rate of change of the
input voltage. A dc input will make
Eo = 0 because of the blocking
The Differential (Subtracting) The Integrating Op Amp capacitor C . A square wave at the
OP Amp input will produce a spike at the out-
The simple integrating op amp shown put triggered by the leading and trail-
If the same signal is applied to both in Figure 13produces an output signal ing edges of the input signal. Because
the +input and the -input of the op proportional to the integral of the the top of the square wave is a con-
amp shown in Figure 12, the two input signal and time variable of the stant value, the differential factor is
amplified output signals will be 180 resistance and capacitance charging zero and the integrating capacitor dis-
degrees out of phase and will com- rate. The capacitor connected across charges towards zero.
pletely cancel each other. Since the the input and output of the inverting
op amp responds only to differences op amp improves the performance by
between its two inputs, it is said to what is called the Miller Effect. The
be a differential amplifier. The voltage Miller Effect says that a capacitor con- The Logarithmic Converter
difference between the +input and nected as shown appears to the input OP Amp
the -input is called the differential as being multiplied by the gain of the
input voltage. Since a differential amplifier. If a nonlinear element such as a trans-
amplifier amplifies only the differen- istor is connected into the feedback
tial input voltage and is unaffected by If R = 1 megohm and C = 1 micro- path as shown in Figure 15, E,, versus
signals common to both inputs, it is farad, according to the formula Eo follows a nonlinear function. The
said to have common-mode rejection. shown in the figure, Eo will increase base-emitter junction of Q, represents
Common-mode rejection can be very
useful, for example, when measuring
at a rate of 1volt per second, positive
or negative, depending on the polar-
the logarithmic element in the feed-
back loop.
-3
4 BENCH BRIEFS WWW.HPARCHIVE.COM 2ND QUARTER 1990
I
Figure 13. Simple integrating operational amplifier
The Antilog O p Amp
By placing the nonlinear element in Figure 14. Simple differentiator
the input path as shown in Figure 16, operational amplifier
the circuit becomes an antilog conver-
ter. For a logarithmic input E*,, the
output E, will be a linear signal.
Multiplication (Division) With
Log-Antilog Operational
Amplifiers
Since log A + log B = log AB, and
log A - log B = log A/B, a circuit
using two log converters and a sum-
ming (subtracting) amplifier, fol-
lowed by an antilog converter, will
output the product or the division of
the two input signals. Figure 17 illus- Figure 15. Simple logarithmic converter Figure 16. Simple antilog op amp
trates the circuit for multiplication. operational amplifier
SUMMING
ANTILOG AMPLIFIER
LOG A + LOG 0
Figure 17. Multiplication circuit using log and antilog operational amplifiers
2ND QUARTER 1990 WWW.HPARCHIVE.COM BENCH BRIEFS 5
TUNECONTROL
POWER SUPPLY SWEEP
- 5 VOLT ADJ v
TUNE BUFFER R21
RlO 1 0 ~ SWEEP + TUNE
6 5000
OUT
-
-
- 15V
Figure 18. Typical op amp application as Typical Op Amp Circuit summing amplifier for the tuning and
an impedance converter (&), isolator
Figure 18 illustrates a typical example sweep voltage.
(U,), and summing amplifier (U,)
op amp application. The task is to pro-
duce and mix a tuning voltage with a If you desire a more detailed and in-
sweep ramp for a YIG oscillator. U6 depth discussion of op amps, I
operates as an impedance converter suggest that you read Understanding
for the zener diode CR1. Rloo pro- IC Operational Amplifiers, by Roger
duces the tuning voltage that is iso- Melen and Harry Garland, available
lated by U7. Finally, U4operates as a from Howard W. Sams & Co. 0
Safety-Related Service Notes
Service notes from HP relating to per- routine dielectric withstand test wires being improperly connected in-
sonal safety and possible equipment (HIPOT). This service note applies to side the transformer. The result is that
damage are of vital importance to our instruments within the serial number when operating on the 220 volt line
customers. To make you more aware range of 2845A00101/2935A00114. If setting, the line fuse blows. Both the
of these important notes, they are you own one of these HP E2500As, line module and power transformer
printed on paper with a red border, you may return it to your nearest HP must be replaced at an HP Customer
and the service note number has an Customer Service Center for the Service Center. Do not attempt to re-
"4" suffix. In order to make you im- HIPOT test, which will be conducted wire the transformer as this will in-
mediately aware of any potential free of charge. validate the color coding used on the
safety problems, we are highlighting wires.
safety-related service notes here with
a brief description of each problem.
Also, in order to draw your attention HP 5347A & 5348A Counter/ Safety Service Notes 5347A-03A-S
and 5348A-03A-S concern the re-
to safety-related service notes in the Power Meters moval of unsafe carrying straps. This
service note index, each appropriate
safety-related service note is high- service note applies to all units. The
lighted with a contrasting color. Safety Service Notes 5347A-02-S and clips on the ends of the carrying
5348A-02-S describe an incorrectly straps, which are part of Option 060
manufactured power transformer. are defective and may fail in the nor-
HP E2500 Frequency Agile The serial numbers affected are mal use of the instrument. Damage
Signal Simulator 2924A00101-158 and 160-170 for the to the instrument and/or injury to per-
HP 5347 and 2924A00101-120 for the sonnel may occur. The defective
Safety Service Note E2500A-01-S de-
scribes how to safety check the
HP 5348. The manufacturing error
concerns the transformer primary
straps are identifiable as being non-ad-
justable in length. Also, there is con-
1
6 BENCH BRIEFS WWW.HPARCHIVE.COM 2ND QUARTER 1990
cern over the strength of the front HP 8340A/B Synthesized mains transformer's insulation.
panel casting at the carrying strap Sweepers
holes. Mis-application of a customer If your instrument is one of the above,
furnished strap may apply sufficient HP 8341A/B Synthesized
please return the unit to an HP Cus-
leverage by weight of the instrument Sweepers tomer Service Center for repair.
to cause breakage. No strap or other HI' 8719A Network Analyzers
carrying appliance should be con- HI' 8720A/BNetwork Analyzers
nected at these points. HP 8757C/E Scalar Network
The following Safety Service Notes Analyzer
Please remove the non-adjustable describe possible injury from falling
strap from the unit and return it to instruments due to damaged front Safety Service Note 8757C/E-02-S de-
the following address. A new adjust- panel handles. scribes a possible defective lithium
able strap will be returned to you, in battery contained on the CPU board
addition to a pair of plastic plugs to 8720A-054, 872OB-Ol-S, 8719A-Ol-S, of the instrument. The battery may
block the front panel carrying strap 8340A-30-S, 8340B-30-S, 8341A-30-S, leak electrolyte and damage the
attachment holes. 8341B-30-S board. Symptoms include yellowing
around the battery or in some cases,
corrosion of the board and other
If damaged handles are used to lift or boards in close proximity. The Safety
Joe Dore 52U/19 support the instrument, the handles Service Note contains a list of applic-
Hewlett-Packard Co. will break causing the instrument to able serial numbers. Please return
5301 Stevens Creek Blvd. fall, possibly resulting in personal in- your unit to the nearest HP Customer
Santa Clara, CA 95052-8059 jury. Exercise caution when using the Service Center for repair.
front handles to lift the instrument.
The damaged handles will be re-
placed at an HP Customer Service
The solution to making the instru- Center, or you may order the front HP 85620A Mass Memory
ment portable is the design of a soft handle replacement kit free of charge Module
carrying case. This case has been de- (HP PIN 5062-3990) and perform the
signed to enhance portability with replacement following the instruc- Safety Service Note 85620A-03-S de-
tough cordura nylon double-stitched tions in the product's service manual. scribes a possible defective lithium
construction that is padded on all six battery contained on the mass mem-
sides. The permanently attached ad- ory module of the instrument. The
justable strap provides a much safer battery may leak electrolyte and dam-
means of carrying the product and al- HP 8657B Synthesized Signal
Generator age the board. Symptoms include yel-
lows easy measurements with the lowing around the battery or in some
unit suspended from the shoulder. cases, corrosion of the board and
Safety Service Note 86578-01-S de- other boards in close proximity. The
scribes a possible shock hazard that serial number range of affected instru-
If you originally purchased the prod- may exist if the instrument's toroidal ments is 0000A00000/3003A00604. If
uct with the Option 060 portability op- mains transformer's insulation has you possess one of the affected units,
tion and have returned the strap as been damaged by the A14 assembly's please return it to the nearest HP Cus-
previously requested, you will receive heatsink. The units affected are tomer Service Center for repair.
this new soft carrying case at no
within the following serial number
charge.
ranges:
HP 86792A Agile Upconverter
If you did not order Option 060 and
wish to buy the soft carrying case, Safety Service Note 86792A-02-S de-
order HP P/N 05348-60214. The price scribes how to safety check the
is $295 U.S. list. routine dielectric withstand test
(HIPOT). This service note applies to
The HP 86578 may present a shock instruments within the serial number
For those customers ordering the in- hazard only if the following condi- range of 2814A00105/2814A00108. If
strument and specifying the portabil- tions exists: you own an HP 86792A within the
ity option, please be advised that Op- serial number range listed, you may
tion 060 has been discontinued. The 0 The mains transformer has not been return it to your nearest HP Customer
r portability option is now the soft car-
rying case and is listed as Option 070,
$295 U.S. list.
manufactured by "NUVOTEM"
and
The A14 heatsink has damaged the
Service Center for the HIPOT test,
which will be conducted free of
charge. 0
2ND QUARTER 1990 WWW.HPARCHIVE.COM BENCH BRIEFS 7
The Logistics Data Book 1990
The Logistics Data Book is designed to and two numbers after the model
assist Hewlett-Packard's government number (e.g., HP 1234A OptionH02).
customers with their logistics needs Modifications and systems may be 0
associated with the support of HI' identified in HP literature with a
products. Information is drawn from single alpha and two digits preceding
HI' records and Department of De- the model number (e.g., E12-1234A).
fense information. It reflects logistics
actions through October, 1989. For procurement purposes, all op-
tions and modifications in this book
The types of HP products covered in follow the model numbers and are
connected to them by hyphens (e.g., 0
this publication include electronic
components, medical instruments 1234-001 and 1234A-E12). Where
and systems, computer equipment, space is limited, option numbers may
calculators, instruments and systems be shortened to less than three charac-
for chemical analysis, and electronic ters (e.g., 1234A-01-02-EI2).
test and measuring systems.
Model numbers are arranged in typi-
cal computer sequence (i.e., left-jus-
The intent of the Logistics Data Book tified, alpha-numeric sequence) so
is to include HP model numbers and that all the "1s" (Model 1, 11, 111,
their various options that are pur- 1111, etc.) are listed before the "2s"
chased by government customers. (Model 2, 22, 2222, etc.).
Additional information on all HP If you h ve any comments or sugges-
parts having National Stock Numbers The Hewlett-Packard office nearest tions about how we can make the
may be found in the microfiche NSN/ you will be pleased to work with you Logistics Data Book more useful to you,
HI' Cross Reference (Publication No. on procurement matters. Also note please let us know by writing to:
5957-4171). that the most currently-produced HP
products are on GSA federal supply
Options are usually identified in HP schedule multi-award contracts, and Hewlett-Packard Co. ,"\
product literature by a three-digit that GSA catalogs are available from U.S. Field Operations
number following the model number your HP office. To order your Logistics John Cloutier
(e.g., HP 1234A Option 003). Other Data Book, specify publication no. 19320 Pruneridge Avenue
options may be designated as a letter 5954-7744. Cupertino, CA 95014 0
What is Traceability and How Does It Relate to Calibration
Uncertainty?
Jim Becktold the standards used to calibrate these able. The desired ratio of accuracy be-
Hewlet t-Packard standards, and so on back to the re- tween a source instrument and one
Traceability is proof that measure- ports issued by national laboratory to be calibrated is 1O:l. If this cannot
ments can be attributed to a national standards. be met, it is permissible to reduce the
standard. The process involves the ratio downward to a lower limit of 4:l.
"tracing" of measurement compari- Calibration uncertainty is the ability
sons made between the instrument to quantify the error sources present This ratio is calculated by dividing the
used and the national laboratory. in the calibration measurement. tolerance of the measurement to be
Technically, traceability involves the Knowing that the act of making mea- made (e.g., 5%) by the tolerance as-
ability to quantify the measurement surements is experimental, there signed to the instrument used to
errors present in the test or measure- have to be some guidelines that tell make the measurement (e.g., 1%). In
ment process in terms of the national the person doing the measurement this example of accuracy, the ratio
standards. Agencies require us to ob- that the job is being performed satis- would be 5:1.
jectively demonstrate that traceability factorily. A rule-of-thumb method
exists. Usually through a series of re- called the "accuracy ratio" is used in In some of today's instrumentation,
ports attesting to the calibration of the
instruments used in a test situation,
many laboratories to determine
whether the uncertainty is reason-
the instrument being calibrated is al-
most as accurate as the source device,
1
8 BENCH BRIEFS WWW.HPARCHIVE.COM 2ND QUARTER 1990
and therefore at a ratio of less than each meter. Figure 1 shows a range
4:l. In this situation, the method of from 97.16 to 97.24 volts, and Figure
C calibration used is called "enhanced
accuracy calibration." To achieve en-
hanced accuracy it is necessary to
2 shows a range from 99.1 to 100.7
volts.
utilize a higher echelon standard dur- When we compare the ranges of the
ing the calibration process. This will two meters we find that meter #1 has
provide as much as another order of a spread of 0.08 volts and meter #2
magnitude to the source equipment, has a spread of 1.6 volts. This defines Figure 1. Reading of Meter #1
which widens the ratio between the meter #1 as having 20 times the preci-
two instruments to maintain a good sion than meter #2 has (i.e., 1.6/.08
confidence level. We recommend that = 20).
when you get below 4:1, contact your
metrologist for advice.
But meter #2 is closer in its readings
A more specific method of determin- to 100.00 volts, which indicates that
ing uncertainty involves understand- precision by itself does not necessarily
ing the types of errors that exist dur- produce accuracy. Meter #2 is more
ing measurement and calibration, and accurate than meter #l.
ways of avoiding the most serious
ones. Now, as shown in Figure 3, if meter Figure 2. Reading of Meter #2
#1 were recalibrated, with adjust-
But before we get into the three types ment, to agree with the "perfect"
of errors, we should define two terms calibration source, the spread of its
used in measurement that are quite readings would likely range from
often confused -accuracy and precision. 99.96 volts to 100.04 volts (a spread
of 0.08 volts). While this shows that
precision and accuracy combine to pro-
Accuracy vide greater confidence in the use of an
The accuracy of a measurement is an instrument, the two are truly inde-
pendent. However, the best of both
rp expression of the closeness of its re-
sult to the true value. A high accuracy are desirable in any measurement
L
Figure 3. Altered Reading of Meter #1
indicates a close approach to the true situation.
value.
Errors in Measurement Systematic Errors
Precision
The precision of a measurement is a There are three types of errors by Systematic errors relate to the in-
measure of its repeatability. A high which you may be confronted. They strumentation or external influences
precision indicates the ability to re- are: gross errors, systematic errors, to the instruments. Systematic errors
peat measurements within narrow and random errors. cause the measured value to be offset
limits. by a fixed amount, as contrasted to
Gross Errors random errors, which are bipolar in
These two definitions form the basis nature.
for everything else that follows rela- These errors are strictly under the
tive to measurement and calibration. control of the individual, totally One example may be loading. All
The ultimate goal is to achieve both separate from the instrumentation. measuring systems are intrusive.
accuracy and precision in every mea- Example of gross errors are: That is, no matter what type of device
-
surement and in every calibration. is used to make a measurement, it
will have some effect on the system
To eliminate the confusion that nor- Misreading the instruments being measured.
mally exists between accuracy and 1 Making an incorrect adjustment
precision, the following example will Consider the fact that no voltage
Applying instruments improperly
-.
1
serve to show the difference. source has the ideal zero impedance,
Computational errors and no current source has the ideal
Recording interpolated data infinite impedance.
Example
r Assume that two meters are used to
measure a perfect 100.00 volt power
source. Ten readings are taken with
As can be seen, these are errors that
can be avoided by care and attention.
A voltage source may have a source
resistance of as little as 0.01 ohm, and
the ability to supply current of 25 mil-
2ND QUARTER 1990 WWW.HPARCHIVE.COM BENCH BRIEFS 9
liamps at 10 volts output. The internal Random uncertainties are of a type tions can be made regarding random
voltage drop could then be 250 micro- that lend themselves to statistical errors:
volts, which represents 25 ppm of the
10 volt output (0.0025%). In addition,
analysis, since they can be considered
to vary either positively or negatively The closest value to the true value /7
assume that the connecting leads around the measured value. They are is the mean value
have 10 milliohms of resistance. The due to totally unknown causes, and 1 It is likely that values close to the
voltage drop across the leads would are detectable when repeated mea- mean value will be more numerous
add another 250 microvolts of error, surements are made with a seemingly than values that are far away from
or 25 ppm. These two elements alone constant set-up and consistent the mean value
constitute an error of 50 ppm, or technique by the user.
0.005%. Note that the obvious way There are likely to be as many read-
to avoid these errors is to use 4-wire An example may be a variation in im- ings that lie above the mean value
remote sensing whenever the load is pedance matching in high frequency as there are those that lie below the
less than 1 megohm. instruments due to changes in charac- mean value
teristics when the lead connectors are
Random Errors removed and replaced. This may be It is the general nature of a measured
due to the wear, or contamination, of variable that there will be a distribu-
These errors are indicated as a scatter BNC connectors, which are quite sus- tion of values (both plus and minus)
about an average when a multiple ceptible to this behavior. around the true, or actual, value.
number of measurements are taken.
This can be the result of variations in When a succession of measurements Note that it is never possible to know
the measuring system, or changes in are made which differ one from the true value, since there will always
the quantity being measured. another, some preliminary observa- be some small error. 0
Important Notice about Service Notes
Service notes contain product-specific Bench Briefs Library 5951-6511
service information for Hewlett-Pack- If you want to order a service note, Update service 5951-6517
ard's electronic products. Subjects in- refer to the list of service notes in the
clude product improvements, modifi- index, find the service note number
cations, and procedures for trouble- belonging to the product you are in- Please note that automatic shipments
shooting, maintenance, and repair. terested in, and note the package of the update service will no longer
Service Notes are published as ap- number. Use the form on the last page be made. If you want to continue to
propriate throughout the life of a of Bench Briefs to order the number receive quarterly updates to the
product. All new notes are an- that appears in the "service note pack- microfiche library, you must place a
nounced in Bench Briefs. age" column. You will receive a pack- new order during the first month of
age of service notes that includes the each quarter (May, August, Novem-
Please note that Hewlett-Packard has one you ordered. ber, February). Note that inventory
restructured the procedure for hand- will be purged at the end of each quarter.
ling and distributing instrument-re- Microfiche
lated service notes through Bench Service notes are still available on Contact your local HP saledservice of-
Briefs and the microfiche program. microfiche. The part numbers are: fice for more information. 0
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1990 Bench Briefs' Instrument
Service Note Index
SN SN Abstract Service Note
Type No. Package
MA 436A-16B Recommended replacement display driver assembly 017
MR 437B-03 Modification to prevent erroneous power meter readings 019
MR 437B-04 Mod. to overvoltage protection circuit 020
MR 438A-10 Recommended A4C14 and A4C16 capacitor replacement to improve performance 017
IO 1630A/D/G-14 Display system components available as a matched set (2090-0227) 021
IO 163lA/D/G-14 Display system components available as a matched set (2090-0227) 021
IO 165OA-09 Repair procedure for POD cable connectors J1-J5 (HP P/N 1251-8158) 017
IO 1650B-01 Repair procedure for POD cable connectors J1-J5 (HP P/N 1251-8158) 017
IO 165lA-09 Repair procedure for POD cable connectors J1-J5 (HP P/N 1251-8158) 017
IO 1651B-01 Repair procedure for POD.cable connectors J1-J5 (HP P/N 1251-8158) 017
MR 3314A-03 Mod. to correct improperly crimped cooling fan power leads 020
IO 3562A-11 Instructions on how to service the HP 3562A Signal Analyzer with Option 063 019
MR 3563A-01 Modification prevents instrument lock-up when using systhesis table 022
IO 3577A-14 Required modification when replacing U13 on the A1 board 022
7 MA 3586A/B/C-13 Modification available when replacing U1 and U29 on A61 board 023
IO 3586A/B/C-14 Instructions on removing the internal Ni-cad battery for extended storage 023
SA 3588A-01-S Notification that the fuse label contains the wrong replacement fuse information 022
MR 3588A-02 Metal flakes settling on the motherboard may cause intermittent H/Werrors 022
IO 3708A-17 Semi-automatic performance test for the HP 3708A 017
IO 3708A-18 Preferred repl. for capacitor A501C5 on the power supply high current assy. 019
IO 3708A-19 Preferred replacement for D/A Converter A204U7 on the Var. Gain Cntl. Assy. 021
IO 3709B-04 Preferred repl. for the Mod. Scheme Switch A3S2 on the microprocessor assy. 019
IO 3746A-34A Preferred repl. for the Fract. N cir. A3OU16) on the Fract. N divided by N assy. 017
IO 3746A-35 Changes to the 3.1 kHz channel filter adjustment 017
IO 3746A-36 Preferred repl. for the 50 MHz crystal (A40Y90) on the A40 Frequency Ref. Assy. 019
IO 3776A-36 Preferred repl. of transistorsA7Q21 and A7Q22 019
IO 3776A-37 Preferred replacement of A3U33 and A204U47 021
IO 3776B-44 Preferred replacement of A3U33 and A204U47 021
IO 3779A-61 Preferred replacement for EPROMS A24, U31 and U41 020
IO 3779A-62 Firmware upgrades 021
IO 3779B-65 Firmware upgrades 021
IO 3779C-12C Preferred repl. board assemblies that comply with VDE specifications 019
MA 3779c-43 Small modification required when replacing A16 Assembly 019
IO 3779c-44 Alternative recommended test equipment for performance tests 021
IO 3779D-12C Preferred repl. board assemblies that comply with VDE specifications 019
MA 3779D-47 Small modification required when replacing A16 Assembly 019
IO 3779D-48 Alternative recommended test equipment for performance tests 021
MA 3787B-04E Newer features can be retrofitted to earlier 3787B instruments 019
3 IO 3787B-09 Notification of