147(Model147Nanovolt_Null) 电路图.pdf

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1、RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 INSTRUCTION MANUAL MODEL 147 NANOVOLT NULL DETECTOR OCOPYRIGHT 1972, KEITHLEY INSTRUMENTS, INC. PRINTED, APRIL 1977, CLEVELAND, OHIO, U. S. A. RadioFans.CN 收音机爱 好者资料库 CONTENTS MODEL 147 CONTENTS Section Page 1. GENERAL DESCRIPTZON- 1 2. OPERATION- 5 3.

2、 APPLICATIONS- 21 4. C1Ianel,. 0572 I GENERAL DESCRIPTION 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 bat

3、tery 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 u

4、sed 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 measur

5、ing small changes in a larger dc signal or compensating for thermal emfs. 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、 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. Keithleys Model 147 is more sensitive than the finest galvanometer systems. It is also immune to mechanical vibrations, thus eliminating the n

7、eed for shock-free mountings. Additional advantages over galvanometer systemsinclude 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 GENERAL DESCRIPTION MODEL 147 FIGURE 2. Fro

8、nt Panel Controls. 0572 MODEL 147 NULL DlXI:ClOR SECTION 2. OPERATION 2-l. FRONT PANEL CONTROLS. (See Figure 2.) a. AC CONNECTI?D Lamp. l:hc Lamp is lit whcncvcr the unit is connected t0 i.lll xi. pwur line and the POWER SUPPLY Switch is in tile AC or OFF position, NOTE b. BATTERY CHARGING Lamp. Whe

9、n lit, this Lanq indicates the ibattery ins clrnr:ini:. p1,: charge current determines its brightness. If the lamp is noi lit, tllc LllC lbilCLtdl. ii charged. c. POGJIZR SUPPLY Switch. Ihe Switch controls tlrc mode of opcratiori for tile powel- suppI!:. 1. AC position: The Null Detector will opcrat

10、c 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 will lbc charged, if nccdcd and if the power cord is connected. 3. BATIERY position: The Null Detector is operating

11、from its battery. IliC ni power line is internally disconnected, whether or nut tile power cord is coluieclcd; the AC CONNECTiXD Lamp is off; the battery cannot be charged. 4. BATT. TEST position: When the POWER SUPPLY Switch is held in this posil:ioii, the Model I.47 shows the state of the battery

12、charge directly on its mctcr. Al I circuits within the instrument are the same as for battery operation exccpl at Lllc meter terminals. POWER SUPPLY 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 Cllnn

13、Ot bc cli;lr:c!d BATTERY Yes Off Battfry cannot IbC char;:ed NO Off Battery cannot hc chnrcd Yes Off BATT TEST Battery can,ot bc cllar:cd NO Off LIattcry cannot be charged TABLE 1. Indicating Lamps and POWER SUPPLY Switch Settings. The Table SllOWS tile relationship between the front panel lamps, th

14、e power cord and the IOliER SUl1I.Y Switch setting. 0365 OPERATION MODEL 147 NULL DETECTOR d. RANGE Switch. 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 funct

15、ion - MICROVOLTS or HILLI- VOLTS - which is to be measured. f. ZERO SUPPRESS Controls. Two controls determine the amount of zero suppression. 1. The COARSE Control disconnects the suppression circuit (in OFF position) or selects one of four suppression voltages in decade steps. Refer to Table 3. 2.

16、The FINE Control is a continuously variable adjustment for the suppression voltage set by the COARSE Control. It adjusts the range between the positive and negative values of the maximum voltage set by the COARSE Control. g. INPUT Receptacle. The INPUT Receptacle is of a special low-thermal design.

17、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 CONTROLS AND CONNECTIONS. a. Line Voltage Switch. The screwdriver-operated slid

18、e 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 gro

19、und connection for the cabinet. An adapter for operation from Z-terminal outlets is provided. 6 0365 MODEL 147 NULL DETCCTOR 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

20、cps, but ac rejection is bcsc at the indicated frequency. Paragraph 2-18 dcscribcs adjustirl; lilf filter circuit. d. DEMODULATOR TEST Jack. A phone jack provides access to LllE denldLllator ior ti.5: purposes. f. OUTPUT. The OUTPUT Rcceptaclc provides iL volt at one! mill.iampcrc f:or a iilll.-scal

21、e 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! i,t is greater than lOlo ohms wit11 the power cord connected. Al.so use battery opernti

22、iln it reduce the 8-cps ripple which may appear at the output with i-11 input shorted in i 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 M

23、ODEL 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, co

24、nnect the power cord to an ac power line. Turn the POWER SUPPLY 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 r

25、echarged at night. Leave the instrument always connected to the ac power line; then turn the POWEK SUPPLY 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:

26、 1010 ohms with the POWER SUPPLY 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: POWER SUPPLY Switch OFF FUNCTION Switch MILLIVOLTS RANGE Switch 100 ZERO SUPPRESS COARSE Control OFF NO

27、TE Make sure the ZERO SUPPRESS COARSE Control 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

28、 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 CONNECTED Lamp will light, asp will the BATTERY CHARGING Lamp if the battery is being charged. If the circuit low is to be at g

29、round, put the shorting link between the LO and GND posts on the rear panel. d. Turn the POWER SUPPLY 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

30、 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 t

31、he circuits 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 I1lYlECTOR 1, , Make sure the signal is greater than Johnson noise in the source resist

32、ance (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 gr

33、ound 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 147 input is with the Model 1481 Low-Ther- mal Input Cable, supplied with the instru- mcnt Use tile Cable for temporary setups, for

34、measurements at several points, and when fast connections are needed. The Mo- del 1481 connects directly to the INPUT 1eceptacl.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 Cab

35、le. 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,

36、 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 poss

37、ible, heat sink all cadmium-soldered joints together to re- duce generated thermal emfs. Careful techniques will keep thermal emfs below 0.1 microvolt. ILCUIW 5 . Model 1483 Low-Thermal Connecti K in t . lieTcr to Section 6 for contents. d. Use crimp connections with copper wire and lugs for the bes

38、t low-thermal joints. Thermal emfs 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 nut

39、s. 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

40、 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

41、 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

42、 14,7 output is no longer grounded. 3. If power line frequency pickup is a problem, battery operation usually provides better results. 2-9. KECORDER OUTPUT. 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 resi

43、stance 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. Synchr

44、onized Buss System for Model 14,7. When two or mre 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

45、 SYSTEM. a. The Model 1.47 oscillator is adjusted for a nominal freqnency ol 94 cps. ,Oi.!iVC1 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.

46、 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 having a fairly higil i

47、mpedance between tllc Cvil instruments. A IlO-volt, low power isolation transformer works wit. USC n 0.5-:nicrv farad isolation capacitor in series with iboth primary and secondary windins o! C!IE i:i,i:- former. d. For several Null Detectors connected together, l,sc a synct,rnizcil bliss :;ysliT!,

48、:iii shown in Figure 6. 2-11. ACCURACY CONSIDERATIONS. For sensitive measurcmcnts - 10 millivolts and bt1lbi.x - other considerations beside tile instrument affect accuracy. i:l:Ifcts not Iroticcnblc ,.i!len working with higher voltages are very important with microvolt signals. Tl,c, lodel vi 7 reads only the signal received at its input; tllcrciorc, it is important tllat this signal be properly transmitted from the source. The fol,iowing paragraphs indicate iactor xiii c:. affect accuracy: thermaI noise , input resistance, thermal emis, shicldilll: iinl