HP-412A-Manual 电路图.pdf

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1、I . : HP Archive . . This vintage Hewlett Packard document was preserved and distributed by www. Please visit us on the web ! . . On-line curator: Tony Gerbic RadioFans.CN 收音机爱 好者资料库 412A DC VACUUM TUBE VOLTMETER SERIALS PREFIXED: 004- RadioFans.CN 收音机爱 好者资料库 OPERATING AND SERVICING MANUAL MODEL 412

2、A DC VACUUM TUBE VOLTMETER SERIALS PREFIXED: 004- Copyright HEWLETT-PACKARD COMPANY 1959 275 PAGE MILL ROAD, PALC ALTO, CALIFORNIA, U. S. A. RadioFans.CN 收音机爱 好者资料库 Page 1 of 2 SPECIFICATIONS Model 412A TOLTMETER Voltage Range: Accuracy: Input Resistance: AC Rejection: MMETER Current Range: Accuracy

3、: Input Resistance: Positive and negative voltages from 1 millivolt full scale to 1000 volts ful scale in thirteen ranges. *l% of full scale on any range. 10 megohms *l% on 30 megohms *l% on 30 mv range. 100 megohms +l% on 100 mv range. 200 megohms *l% on 300 mv range and above. 1 mv, 3 mv, and 10 m

4、v ranges. A voltage at power line or twice power line frequency 40 db greater than ful scale affects reading less than 1%. Peak voltage must not exceed 1500 volts Positive and negative currents from 1 microampere full scale to 1 amperc full scale in thirteen ranges. *2% of full scale on any range. I

5、nternal Shunt Full Scale Internal Shunt Full Scale Range Resistance* Voltage Drop Range Resistance* Voltage Drop .001 ma 1000 ohms 1 mv 1 ma 1 ohm 1 mv .003 ma 316 ohms 0.9486 mv 3 ma 0.316 ohm 0.9486 mv .01 ma 100 ohms 1 mv 10 ma 0.1 ohm 1 mv .03 ma 31.6 ohms 0.9486 mv 30 ma 0.1 ohm 3 mv .1 ma 10 o

6、hms 1 mv 100 ma 0.1 ohm 10 mv .3 ma 3.16 ohms 0.9486 mv 300 ma 0.1 ohm 30 mv 1000 ma 0.1 ohm 100 mv * For total insertion resistance add 0.07 ohms copper lead resistance at 25OC. 7 Model 412A SPECIFICATIONS (CONTD.) Page 2 of 2 OHMMETER Resistance Range: Resistance from 1 ohm centerscale to 100 mego

7、hms centerscale in nine decade ranges. *5% of reading from 0.2 ohm to 500 megohms. 510% of reading from O.lto 0.2 ohm and from 500 megohms to 5000 megohms. Accuracy: Open Circuit Short Circuit Open Circuit Short Circuit Voltages and Currents: Range Volts Current Range Volts Current x1 10 mv 10 ma Xl

8、OK l v 100 Fa x10 100 mv 10 ma XlOOK l v 10 Fa XlOOO l v 1 ma XlOM l v .1 pa XlOOM l v .01 pa XlOO l v 10 ma X1M l v 1 Fa AMPLIFIER Voltage Gain: AC Rejection: output: Output Impedance: Noise: Drift: GENERAL Isolated Input: Power: Dimens ions : 1000 maximum Approximately 3 db at 1 cps, 80 db at 50 a

9、nd 60 cps. Proportional to meter indication; 1 volt at full scale. (Full scale corre- sponds to 1.0 on upper scale.) Less than 2 ohms at 0 cps. Less than 0.1% (rms) of full scale on any range. Negligible. Input terminals are isolated from case (power line) ground by a minimum leakage resistance of 1

10、00 megohms shunted by 0.1 Ff. Maximum potential difference between common Iead and case ground: 500 v peak. 115/230 volts *lo%, 50-60 cps, 35 watts. Cabinet Mount: 11-1/2 in. high, 7-1/2 in. wide, 10 in. deep. Rack Mount: 5-1/4 in. high, 19 in. wide, 10 in. deep. Weight: Cabinet Mount: Net 12 Ibs.,

11、shipping 17 Ibs. Model 412A CONTENTS SECTION I GENERAL DESCRIPTION General . 1 - 1 1 - 3 Power Cable . . . . . . . . . . . . . . . . . . . . . . . . . 1 - 2 Damage in Shipment . 1 - 4 230 Volt Operation . . . . . . . . . . . . . . . . . . . . . . SECTION I1 OPERATING INSTRUCTIONS 2 - 1 Low-Level Ele

12、ctrical Phenomena . . . . . . . . . . . . . 2 - 2 Operating Instructions . SECTION I11 CIRCUIT OPERATION 3 - 1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2 Circuit Operation . . . . . . . . . . . . . . . . . . . . . . SECTION IV MAINTENANCE 4 - 1 4 - 2 4 - 3 4 - 4 4 - 5 4 - 6

13、4 - 7 4 - 8 4 - 9 4 . 10 4 . 11 4 . 12 Introduction . Required Test Equipment . . . . . . . . . . . . . . . . . . Performance Check . Cabinet Removal . Adjustments . Tube Replacement . Trouble Shooting . Modulator Check . Modulator Replacement . . . . . . . . . . . . . . . . . . . Demodulator Check

14、. Demodulator Replacement . . . . . . . . . . . . . . . . . Cable Replacement . SECTION V TABLEOFREPLACEABLEPARTS 5 - 1 Table of Replaceable Parts . . . . . . . . . . . . . . . . . Page 1 - 1 1 - 1 1 - 1 1 - 1 I1 . 1 I1 . 1 I11 . 1 I11 . 1 IV . 1 IV . 1 IV . 1 IV . 3 IV . 3 IV . 4 IV . 4 IV . 4 IV .

15、 5 IV . 5 IV . 6 IV . 6 v - 1 Model 412A 1-1 GENERAL The Model 412A DC . xuum Tube Voltmeter is a precision, wide range, multipurpose instrument which covers the entire range of voltage, cufrent, and resistance measurements normally encoun- tered in electronic equipment. It measures volt- ages from

16、less than 0.1 millivolt to 1000 volts, currents from less than 0.1 microampere to lam- pere, and resistances from 0.02 ohm to 5000 meg- ohms. 1-2 DAMAGE IN SHIPMENT Inspect and operate this instrument upon receipt. Section IV includes a performance check which is a good test as part of incoming qual

17、ity control in- spection. The check can be made with the instru- ment in its cabinet. If there is any damage, see the “Claim for Damage in Shipment” paragraph at the rear of this manual. 1-3 POWER CABLE The three-conductor power cable supplied with this instrument terminates in a polarized three-pro

18、ng Sect.1 Page 1 SECTION I GENERAL DESCRIPTION male connector recommended by the National Elec- trical Manufacturers Association. The third con- tact is an offset round pin added toa standard two- blade connector. This contact grounds the instru- ment when used with an appropriate receptacle. An ada

19、pter should be used to connect the NEMA plug to a standard two-contact output. When the adapter is used, the ground connection becomes a short lead from the adapter. This lead should be connected to a suitable ground for the protection of operating personnel. 1-4 230 VOLT OPERATION The 412A is norma

20、lly wiredat thefactoryfor oper- ation from a 115 volt, 50-60 cps power source. To convert it for use from a 230 volt, 50-60 cps power source, change the dual 115 volt primary windings of the power transformer from a parallel combination to a series combination. See sche- matic diagram for details. A

21、t the time of conver- sion, change line fuse from 1/2 ampere, slow- blow type to 1/4 ampere, slow-blow type. Model 412A Sect.11 Page 1 SECTION II 2-1 LOW-LEVEL ELECTRICAL PHENOMENA Stray low-level electrical phenomena are present, in one form or another, in nearlyall electrical cir- cuits. The 412A

22、does not distinguish between stray and signal voltages; it measures net voltage. Thus, when using the lower voltage ranges, consider the possibility of low-level electrical phenomena. Thermocouples (thermoelectric effect), flexing of coaxial cables (triboelectric effect), apparent re- sidual charges

23、 on capacitors (dielectric absorp- tion), battery action of two terminals mounted on an imperfect insulator (galvanic action) all can pro- duce voltages within the range of the 412A. The 412A voltage probe, current/resistance lead, and common lead are designed to have a very low thermoelectric effec

24、t with copper, the most com- mon electrical conductor. However, you may en- counter other materials. For example, the leads of many transistors are made of a mixtureof iron, nickel, and cobalt known commercially as Kovar, Fernico, etc. This material makes a very good thermocouple with copper: about

25、40 1-1 v/OC with respect to a reference junction. Whenever possible, connect the 412A leads to copper and maintain the points of connection at the same temperature, preferably ambient temperature.With the leads so connected, any voltage indicated by the 412A is developed within the circuit under tes

26、t. 2-2 OPERATING INSTRU CTI O N S CAUTION Do not overload the instrument. Amplifier input, current shunts, and internal resistance standards are not protected from extreme overload. Momen- tary overloads ten times full scale will notdamage the instrument. - - OPERATING INSTRUCTIONS Turn the 412A on

27、and allow a few minutes warm up. A. VOLTAGE MEASUREMENT 1) Set FUNCTION selector to VOLTS. 2) Set POLARITY switch to desired polarity. 3) Set RANGE switch to desired range. 4) Use VOLTS and COM leads to connect instru- ment across circuit or component, and read voltage. B. CURRENT MEASUREMENT 1) Set

28、 FUNCTION selector to MA. 2) Set RANGE switch to desired range. 3) De-energize circuit to be tested. 4) Use MA/OHMS and COM leads to connect in- strument into circuit. 5) Energize circuit, set POLARITY switch for up- scale reading, and read current. NOTE When measuring current, be sure there is no c

29、on- nection between the chassis-ground and cabinet- ground terminals of the DC AMPLIFIER OUTPUT connector. - - C. RESISTANCE MEASUREMENT 1) Set FUNCTION selector to OHMS. 2) De-energize circuit to be measured. Sect. I1 Page 2 Model 412A 3) Use MA/OHMS and COM leads to connect in- strument across cir

30、cuit or component. 4) Select range which brings meter pointer as close as possible to midscale, and read resistance. When measuring the resistance of non-linear de- vices such as crystal diodes or transistors, you may want to know the voltage applied to the device and/or the current through it at th

31、e time of mea- surement. By using Table 2-1 and the upper volt- age scale on the meter face, you can determine both. The meter reading is directly proportional to the voltage across the device being measured, and the meter reading subtracted from full scale is directly proportional to the current. F

32、or example, on the X10 range the upper voltage scale is a 0-100 mv scale and a 10-0 ma scale. If the meter indicates .25 on the resistance scale, the device being mea- sured has an equivalent resistance of 2.5 ohms. But the meter also indicates .2 on the upper voltage scale; thus, from Table 2-1, th

33、e device has 2.5-ohms equivalent resistance with 20 mv across it and 8 ma flowing through it. D. OPERATION WITH A RECORDER To obtain permanent records of 412A readings, connect a recorder to the DC AMPLIFIER OUTPUT connector and operate the 412A as directed above. The output of the 412A is 1 volt at

34、 full scale; if necessary, externally attenuate the 412A output to match it with recorder sensitivity. Maximum rated load current from the 412A is 1 ma. A load resis- tance of less than 1000 ohms may cause the load current to exceed 1 ma and thus cause errors in meter indication and amplifier gain.

35、TABLE 2-1. RESISTANCE RANGE VS OPEN-CIRCUIT VOLTS/SHORT-CIRCUIT CURRENT Range x1 x10 XlOO XlOOO XlOK XlOOK X1M XlOM X 1 OOM Open Circuit Volts (1.0 on upper voltage scale) 10 mv 100 mv l v l v l v l v l v l v l v Short Circuit Current (0 on upper voltage scale) 10 ma 10 ma 10 ma 1 ma 100 pa 10 pa pa

36、 0.1 pa 0.01 ua Model 412A Sect. 111 Page 1 3-1 GENERAL The 412A is basically a 0 to 0.9 millivolt dc volt- meter. Precision voltage dividers, shunts, and reference resistors extend the range of the basic voltmeter and permit current and resistance mea- surements as well. 3-2 CIRCUIT OPERATION With

37、the FUNCTION selector and RANGE switch properly set, voltage is applied to a photoconductive modulator through a low-pass filter. See Figure 3-1. The filter attenuates ac components present on any input signal, and the modulator converts the remaining dc component to a square wave. A synchronous - m

38、otor-driven, light - beam chopper SECTION 111 CIRCUIT OPERATION sets modulator frequency at 5/6- power-line fre- quency. An ac-coupled amplifier amplifies modu- lator output about 500,000 times. A demodulator synchronized with the modulator by the light-beam chopper, converts amplifier output to dc.

39、 The output of the demodulator is filtered and applied through a cathode follower to 1) a feedback network 2) the DC AMPLIFIER OUTPUT terminals and 3) an output indicator. The feedback network sta- bilizes the dc gain of the modulator-amplifier- demodulator system to a value of 1111, thereby providi

40、ng an output of 1 volt for an input of 0.9 millivolt. The output indicator is a 0-1 voltmeter. The POLARITY switch permits reversal of indi- cator connections, if required, to obtain up-scale readings. The POLARITY switch is disabled when the FUNCTION selector is set to OHMS. I I - , AIRTDN SHUNT ,

41、7 I I FEEDBACK NETWORN INTERNAL RESISTANCE a STANDARDS I m t I 0 COMMaV LEA0 Figure 3-1. Model 412A Block Diagram Sect.IV Page 0 Excessive heat or pressure lift the copper strip from the board. Avoid damage by using a low power soldering iron (50 watts max- imum) and following these instructions. Co

42、pper that lifts off the board should be cemented in place with a quick drying acetate base cement having good electrical insulating properties. Use only high quality rosin core solder when repairing etched circuit boards. NEVER USE PASTE FLUX. After soldering, clean off any excess flux and coat the

43、repaired area with a high quality electrical varnish or lacquer. A break in the copper should be repaired by soldering a short length of tinned copper wire across the break. When replacing tube sockets it will be necessary to lift each pin slightly, working around the socket several times until it i

44、s free. Model 412A SERVICING ETCHED CIRCUIT BOARDS 1. Apply heat sparingly to lead of part to be re- placed. Remove part from card as iron heats the lead. 3. Bend clean tinned leads on new part and care- fully insert through holes on board. 2. Using a small awl, carefully clean inside of hole left b

45、y old part. 4. Hold part against board and solder leads. Avoid overheating the board. Model 412A 4-1 INTRODUCTION This section contains testing and servicing infor- mation. Included is a performance check to verify proper instrument operation. The check can be made with the instrument in its cabinet

46、 and is a good test as part of routine maintenance or incoming quality control inspection. Standard, readily available components are used for manufacture of instruments whenever pos- sible. Special components are available through your local Representative who maintains a parts stock for your conve

47、nience. When ordering parts, specify instrument model and serial number plus the component description and stock number appearing in the Table of Replaceable Parts. Your local ($3 Representative maintains complete facilities and specially trained personnel to assist you with any problems you may hav

48、e with instru- ments. 4-2 REQUIRED TEST EQUIPMENT To carry out the instructions in this section, you will need the following test equipment: 1) A dc voltmeter with an input resistance of at least 100 megohms to measure voltages from 1 volt to 350 volts. You can use a voltmeter with 20,000 ohms/volt sensitivity, but circuit loading will cause errors in some