HP-456A-Manual 电路图.pdf

《HP-456A-Manual 电路图.pdf》由会员分享，可在线阅读，更多相关《HP-456A-Manual 电路图.pdf（24页珍藏版）》请在收音机爱好者资料库上搜索。

1、HP Archive This vintage Hewlett Packard document was preserved and distributed by www. Please visit us on the web ! Thanks to on-line curator: Kenneth Kuhn for supplying and scanning this vintage document. RadioFans.CN 收音机爱 好者资料库 5 AC CURRENT PROBE SERIALS PREFIXED: 103- OPERATING AND SERVICING MANU

2、AL , PRINTED 3/61 00395-1 RadioFans.CN 收音机爱 好者资料库 OPERATING AND SERVICING MANUAL MODEL 4 5 6 A SERIALS PREFIXED: 103 - AC CURRENT PROBE HEWLETT-PACKARD COMPANY Mall ROAD. P +5%, 60 cps to 4 mc; -3 dh at 25 cps and greater than 20 mc. Rise time is less than 20 nanoseconds, sag is less than 16% per mi

3、lli- second. 1 amp rms; 1.5 amp peak. 100 ma above 5 mc. No appreciable effect on sensitivity and distortion from dc current up to 0.5 amp. (Impedance added in series with measured wire by probe.) Less than 50 milliohms in series with 0.05 ph. (This is approximately the induc- tance of 1-1/2 inches

4、of hookup wire.) Approximately 4 pf added from wire to ground. For 1/2 amp input at least S O db down. For 10 ma input at least 70 db down. Less than 50 pa rms (100 pa when ac powered). 220 ohms at 1 kc. Approximately +1 volt dc component. Should work into load of not less than 100,000 ohms shunted

5、by approximately 25 pf. Two Mallory Battery CO. TR 233R and one TR 234 batteries stock # 1420-0005 and 1420-0006), battery life is approximately 400 hours. AC power supply optional at extra cost, 115/230 volts +lo%, 50 to 1000 cps, approximately 1 watt. Net 3 Ibs. 5 in. wide, 6 in. deep, 1-1/2 in. h

6、igh. Probe cable is 5 ft long, output cable is 2 ft long and terminated with a dual banana plug. 456A-95B AC Supply for field installation. 1-0 00395-1 Model 456A Section 1 Paragraph 1-1 SECTION I GENERAL I N F O R M A T I O N 1-1. GENERAL DESCRIPTION. The Model 456A is an instrument for measuring a

7、c current. It consists of a probe and amplifier, and is used together with an associated voltmeter or oscil- loscope (see figure 1-1). I ,Conductor measured Figure 1-1. General Arrangement of Model 456A Current is measured by merely clamping the probe of the Model 456A around the current carrying co

8、nductor. The probe operates with an accompanying small ampli- fier to convert the ac current beingmeasured to a pro- portional voltage. The current-to-voltage conversion factor is 1 millivolt output for 1 milliampere flowing through the probe. Current readings can thus he taken directly from the vol

9、tage calibrations on the voltmeter or oscilloscope. Table 1-2 is a list of instruments which can be used with the probe. Table 1-2. Instruments for use with 456A AC Current Probe Voltmeters 400D 400H 400L 403A Wave Analyzer 302A Oscilloscopes 120A 122A 130B 150A 1608 170A Figure 1-2. Model 456A AC C

10、urrent Probe 1-1 00395-1 Section 1 Paragraph 1-2 For flat frequency response the shunt input impedance of the associated voltmeter or oscilloscope should be greater than l00K ohms in parallel with 25 pf or made to appear that value to the 456A. Lower shunt resistance will change the accuracy equally

11、 at all frequencies, due to the low output im- pedance (about 200 ohms) of the Model 456A. Different shunt capacitances have no effect on the low frequency response, but can affect the high frequency gain as shown in figure 1-3. Model 456A -6 1 MC 10 MC 30 MC Figure 1-3. Typical Change in Frequency

12、Response with Load Capacitance The Model 456A output contains a dc component of approximately +1 vdc which must not be loaded ex- cessively (less than 10Kohms shunt load is excessive). Almost all ac voltmeters and oscilloscopes have a dc blocking capacitor in the input circuit to take care 1-2 of th

13、is requirement. DO NOT USE THIS INSTRU- MENT WITH RECTIFIER TYPE METERS. The loading in this type of instrument is excessive and may affect the reading. 1-2. POWER REQUIREMENTS. The Model 456A is available either as a battery powered or ac powered instrument. The AC Power Supply( stock #456A-95B) fi

14、ts into the space nor- mally occupied by the battery supply and takes the place of it electrically. The ac power supply must he ordered separately. When the 456A is powered with its own internal bat- teries it is independent of power lines. It may be used in the field with battery operated voltmeter

15、s, such as the Model 403A AC Voltmeter, or battery powered oscilloscopes. Battery operation is also useful in the laboratory where complete isolation is desired. While battery operated the 456A may be used with the chassis off ground without difficulty. This type of operation may also be desired to

16、isolate power line hum in a system where several instru- ments are used. When the 456A is used with the ac power supply the chassis is automatically grounded through the third prong in the power plug. The three conductor power cable supplied with the instrument is terminated in a polarized, three-pr

17、ong male connector recommended by the National Electrical Manufacturers Association (NEMA). The third conductor grounds the instrument chassis for protection of the operating personnel. WARNING When using a three-prong to two-prong adapter ground the third lead (green wire) externally. 00395-1 Model

18、 456A Section 1 1 Paragraphs 2-2 to 2-5 SECTION II OPERATING INSTRUCTIONS 2-1. GENERAL. The Model 456A must be used with an ac voltmeter or an oscilloscope. Figure 2-2 shows a typical setup. 2-2. OPERATING INSTRUCTIONS. Connect the shielded plug of the Model 456A OUTPUT cable to a voltmeter or oscil

19、loscope of appropriate range. The conversion ratio is millivolts out equals milliamperes in. Thus the voltmeter should read in millivolts the expected milliamperes being measured. The current range of the Model 456A is less than 1 milliampere to 1 ampere. The Model 400D/H/L Vacuum Tube Voltmeter is

20、ideal for this measurement as it covers the entire range and has a 3/4 inch spac- ing input jack. WARNING DO NOT PLUG THE OUTPUT CABLE OF THE 456A lNTO A SOURCE OF AC OR DC VOLTAGE. Doing so will burn out the tran- sistors and perhaps other components. The spacing of the pins on the OUTPUT cable fit

21、s all standard 3/4 inch connectors, such as on Hewlett- Packard voltmeters, wave-analyzers, and oscillo- scopes (when used with AC-76A adapter). See table 1-2 for a list of Hewlett-Packard instruments suitable for use with the Model 456A. The Model 400D has an additional output terminal for viewing

22、the voltage being measured with an oscil- loscope. This may be very useful, for example, measuring the current at which a transistor starts clipping. The Model 456A may be used to measure very low current, even below the noise level of the probe, if some provision is made to filter out the noise. Th

23、e Model 302A Wave Analyzer is ideal for this purpose, particularly if the BFO of the 302A is used as the signal source (see figure 2-1). Transistor under test -hp- 302A WAVE ANALYZER BFO OUTPUT -hp- 456A 20 -50KC CURRENT PROBE Figure 2-1. Probe can he used with 302A to measure distortion in current

24、waveforms or to measure small audio current, as described in text 00395-1 In this manner, currents even below 10 microamperes can be measured. 2-3. OPERATING THE PROBE. The probe jaws may be operated withonehand. While holding the probe handle in the palm, squeeze the flanges together with the finge

25、rs. This action will open the jaws. Move the probe to the vicinity of the insulated wire being measured and slowly release the flanges until the jaws fit over the wire. CAUTION Do NOT let the jaws snap closed as they may he damaged. Clip the probe over the wire with the arrow on the probe in the dir

26、ection of conventional current flow for a positive-going output signal. This procedure is important when using an oscilloscope but it may also be important when using this probe tomeasure unsym- metrical waveforms with half-wave rectifier type meters. All Hewlett-Packard meters listed in table are f

27、ull-wave rectifier types so you will get the same reading whichever way the probe is clipped over the wire. However, with half-wave type meters the readings may be different. This action is a limi- tation of the meter and not a fault of the Model 456A. Refer to the Operating and Servicing Manual for

28、 the meter or change to one of the recommended meters. 2-4. INCREASING THE SENSITIVITY. Sensitivity of the Model 456A may be increased by looping the wire carrying the current to be measured through the jaws more than once. The reading on the meter or oscilloscope will he multiplied by the number of

29、 times that the current passes through the jaws. To obtain the true reading divide the current indication by the number of turns enclosed by the jaws. The series loading effect of the probe on the circuit being measured is then multiplied by the square of the number of turns. This effect may have to

30、 be taken into account (see paragraph 2-5D). 2-5. MEASUREMENT PRECAUTIONS. Best performance will be achieved by observing the following precautions: A. PROBE HANDLlNG 1) Do not snap the jaws closed by letting go of the probe flanges abruptly. This action may damage the shield or the jaws. 2) Do not

31、drop the probe. The jaws are made from an 2-1 Section 1 1 Figure 2-2 Model 456A INSULATED CONDUCTOR BEING MEASURE0 1. Connect output of 456A to a voltmeter or oscil- loscope. 2. Clip probe around wire under test (open jaws by squeezing flanges on probe together). 3. Connect ground-clip to instrument

32、 under test, if necessary (see paragraph 2-5E). 4. Read current being measuredon meter or oscil- loscope (read millivolts as milliamperes). 5. Note direction of arrow on probe. Conventional current flow in direction of arrow gives positive going output voltage. Figure 2-2. Operation 2-2 00395-1 Mode

33、l 456A Section 1 1 Paragraph 2-5 (Contd) Figure 2-3. Cleaning Probe Jaws alkyd material which is very durable in normal use, but is not made to withstand the shock of dropping. 3) Keep the probe jaws clean. If the jaws appear dirty or if the low frequency responsedropsoff, clean the jaws as shown in

34、 figure 2-3 using carbon tetra- chloride and the brush provided or, in extrerne cases, a pencil eraser. The probe jaws should mate perfectly with no air gap between the ferrite pole pieces. Foreign matter (dirt specks, wax from capacitors, sand particles, pieces of insulating tape etc.) may hold the

35、 pole pieces from closing perfectly. Normally the only effect will he to lower the gain at low frequencies (below 10 kc). Even as small an air gap as 0.0005 inch will lower the gain significantly at low frequencies. 4) Always clip the probe around insulated wire. If you must measure the current in a

36、 bare wire, first insulate the wire with tape or insulating tubing. 5) Do not expose the probe to high temperatures. Exposure to temperatures above 55oC is not recom- mended. B. DlRECT CURRENT IN THE SIGNAL BElNG Direct current in the signal being measured should preferably be kept below 1/2 ampere.

37、 Direct current below that value will have no effect on the measurement. MEASURED. C. ALTERNATING CURRENT FIELDS. The probe is shielded against external ac magnetic and electric fields. Extremely strong fields may cause an erroneous reading. If a strong ac magnetic field 00395-1 is suspected, rotate

38、 the empty probe head with the jaws closed. If the reading changes, an ac field is affecting the probe. D. GROUND LOOPS. With the ac supply avoid ground loops in test setups, such as those produced between the third prong on the ac cable and the ground on the indicating instrument. An easy method of

39、 test- ing for ground loops is to clip the probe over the 456A output cable. Any reading indicates the presence of ground loops. OTHER EQUIPMENT SET-UP BEING TESTED POWER I I LINES I_- - * POWER LINE Figure 2-4. Illustrating Development of Ground Loops Referring to figure 2-4, note that the leakage

40、current I-leakage causes a voltage drop across the groundlead resistance This appears as a voltage, in ad- dition to the signal voltage, between the ac current probe Z1 and the indicating device Z2. An easy way of minimizing this problem is to connect both instru- ments to the same ac receptacle. An

41、other method is to use a battery-powered Model 456A. 2-3 Section II Paragraph 2-6 E. EFFECT OF PROBE ON CIRCUlT BEING MEASURED. The probe adds an inductance of less than 0.05 microhenries to the circuit under test. With almost all conditions this small an inductance will not affect the measurement.

42、Model 456A However, if the measurement is made in a very low capacitance and very high impedance circuit, with high ac voltages, and at high frequencies, the shunt capacitance of the probe to ground must be taken into consideration. A capacitance is added from the meas- ured wire to the grounded shi

43、eldinside the 456A probe when the probe is clamped around the wire. This capacitance typically has a value anywhere from 1 pf to 5 pf, depending upon wire size, insulation and location within the probe aperture. This capacitance has two effects: 1) The measured wire is slightly “loaded” with a capac

44、itance to ground of around 3 pf. 2) The capacitive current which flows to ground through this wire-to-probe capacitance can be meas- ured by the probe, although it almost always adds a negligible amount to the reading of the actual cur- rent in the wire. To test if this effect should he considered,

45、solder one end of a short, stiff, piece of insulated wire to the circuit at the point where the measurement is to be made. Leave the other end of this wire unconnected. This wire will have voltage on it but no current through it. Clip the probe over this wire and read the meter. Reverse the directio

46、n that the probe is clipped on the wire (point arrow on probe in other direction) and read meter again. If there is no reading on the meter in either of these positions the probe capacitance has no effect. If there is a reading proceed to the next paragraph. The shunt capacitance introduced by the p

47、robe is 1 to 5 pf (typically 3 pf). Assuming the worst case of 5 pf, a maximum error current of: I = 0.03 ma X volts X megacycles can flow through the 5 pf to ground. That is, a 1 mc voltage of 1 volt impressed across this shunt capaci- tance will cause a reading of only 0.03 ma by the 456A. However

48、, at higher frequencies the effect will increase proportionally. Even with this effect you may choose which side of the circuit to measure the current. See figure 2-5. Note in figure 2-5 the probe measures the current flowing in the circuit on the same side as the wide side of the arrow on the probe

49、. Occasionally at high frequencies (above 15 mc) a greatly magnified voltage effect exists at a particular frequency. This effect is caused by a resonance be- tween excessive external ground lead lengths and stray capacities. The following steps are suggested to eliminate this type of problem: 2-4 THE PROBE AND WIRE BEING MEASURED HAS AN EQUIVALENT CIRCUIT OF: THIS CURRENT THIS CURRENT I NOT MEASURED MEASURED /- I I To 5pF RO PR