Страница 1: ...OPERATING INSTRUCTIONS EB 2700 for Universal Bridge TF 2700 Copyright 1962 MARCONI INSTRUMENTS LIMITED STo ALBANS HERTFORDSHIRE ENGLAND C P lk EB 2700 3 66 K 19 3 66 ...
Страница 2: ... theInterna11 kc s Source 15 l 5 l using anExterna1A F Source 16 l 5 3 IncrementaI Inductance and use of Polarizing Bias 16 l 6 Resistance Measurements o lO l 6 1 usingtheInternallkc sSource II l 6 l using anExternal A F Source o II l 6 3 using the InternaI Battery II l 6 4 usinganExterna1D C Source o l3 l 7 Connectionof Externa1A C Source o l5 l 8 LossBalance QorD l7 3 CIRCUITSUMMARY l8 3 1 Bridg...
Страница 3: ...urements The detector has been designed to have a usable response from 20 c s to 20 kc s This allows an external source to be used to energize the bridge far measure menta aver a more representative range of frequencies D C voltages higher than that of the battery may alBo be applied externally or improved discrimination with re sistance measurement Another facility enables a d c bias to be applie...
Страница 4: ...Accuracy 1 1 of reading 1 0 1 0of range full scale Inductance Additional 0 2 0 of reading 0 0 3 I1H First Ranges only Capacitance 100 I1F 201 f d 1 1 F to 1100 I1F I IOo rea lng jJ Inductance 0 2jJ H 2 0 10 0of reading 0 O 3jJ H dependent to lljJ H upon Q Resistance lO 201 f di 1 1 n l I IO o rea ng LLA to l a Residuals to be COI approx O l pF subtracted Lo approx 0 2 jJ H Ro approx 2 BRIDGE SOURC...
Страница 5: ... improve the d c sensitivity at range extremes For low d c R values a sensitive galvanometer is alBo required FACILITIES A polarizing voltage may be applied to the component under test Non linear elements may be tested by applying a variable d c bias or a f signal POWER SUPPLY InternaI 9 V battery world standard type usual current drain approx 7 mA DIMENSIONS WEIGHT Height Width Depth Weight 8 in ...
Страница 6: ...nge 100 mH to 100 H It is fitted with spade ended leads far connecting to the bridge termina1s Errors introduced by the Adaptor do not genera11y exceed 3 and may be eliminated by simple substitution methods Isolating Transformer Type TM 71Z0 This is intended far connection between the bridge and an externa1 a f energizing source in arder to keep the bridge isolated from earth 6 ...
Страница 7: ...rsa Failure to obtain a complete balance null during a c measurements may be for one or more of the foliowing reasons R Too much stray capacitance or inductance C and L Incorrect adjustment of the LOSS BALANCE partic ularlyat low Q or high D sett_ings This may be due to the limited resolution of the contrai at Q lese than l Alternatively it may mean that the loss of the test component is too compl...
Страница 8: ...mediate divisions of 0 002 The overall calibration is therefore O to aver 1 1 examples of BALANCE contraI readings are given in Fig 2 l c o s o 00604 QJ c o 0 0 Fig 2 l BaIance ContraI Indication The table of range full scale values is linked to the BALANCE controls by the RANGE MULTIPLIER switch The correct impedance value is obt ained by multiplying the BALANCE contraI reading by the fun scale v...
Страница 9: ...e balance indication When measuring large items or componente it is important to avoid the introduction of external interference signals via the DET YE terminaI or else a poor or false balance will be obtained li the component has an isolated screen it is probably best to connect this to the VE chassis terminaI but in the event of this screen having too large a capacity say aver 200 pF to the cont...
Страница 10: ... i i Fig Z 3 Controls and Operational Facilities IO ...
Страница 11: ...9 v 1 1 dO t t3 um z G HOO o m o o O IO In 1 1 m O Io m vm 1 1 Il o N O r CC O Z O o O l n I I Q O O O A U G G 0 G E G 0 V 0 0 O Z e e s u o G e E 1 O O O 0 u v U O m o G U 0 m m v G m_ Q Jd Q o Q m o 8 G Q ZE Q O U U m m N m X o O G Q Q G eO O O Q e G Q O O 9 O t Q e bOO u v A Q o UQ Q G G bOmO m G o O m Dm o d O 5bO U E Q 4 D 0 Q Ee lo u s e G e O O V m e o Q 00 O m 1 1 u Q 00 z u U j m s O OQ G...
Страница 12: ...LTIPLIER switches 3 Set the D Q switch to D x 01 far normal capacitors and to D x l far electrolytics 4 Set the LOSS BALANCE contrai to about l and set the SENSITIVITY contrai to give a meter deflection of lese than full scale 5 Bala nce the bridge with the main BALANCE and LOSS BALANCE controls increasing the sensitivity to keep the meter defl ction above zero until the SENSITIVITY contrai is ful...
Страница 13: ...rolytic capacitors often have relatively large series and paral1elloss components The series 10ss is usually greater and so the D setting of the LOSS BALANCE controls should be used this being essential when a polarizing voltage is applied The LOSS BALANCE adjustment may be found to be rather criticaI therefore the sensitivity should be reduced in arder to obtain a more satisfactory balance Too hi...
Страница 14: ...ge When an external 3 c source is al so being used it will be internally connected to the positive side of the bias supply If however measure ments of an earthed capacitance are to be made it may be more convenient if the two jack plugs are inter changed WARNING l The bridge case is connected to the positive side of the bias supply via the BALANCE resistors O to l OOa and the EXT A C socket Note a...
Страница 15: ...o be made 2 5 l MEASUREMENTS USING THE INTERNAL l kc s SOURCE l Connect the component to the test terminals 2 Select the range full scale appropriate to the expected value of inductance with the FUNCTION and RANGE MULTIPLIER switches 3 Set the D Q switch to i Q far air cored coils ii D x 01 far high Q filter coils iii D x l far laminated iron cored inductors 4 Set the LOSS BALANCE contrai to about...
Страница 16: ...low enough not to affect the balance indication The amount of pick up may be checked by inserting an open circuited jack plug into the EXT A C socket this will switch off the oscilla tor so that only pick up will be detected The residual meter indication shou1d be very low Magnetic cores al so have non linear char acteristics so that a true balance is difficult to obtain U se only sufficient sensi...
Страница 17: ...tip positive sleeve negative Since the bias current alBo flows through the range resistor the oscillator transformer and the external a c supply if being used the permis sible current is limited by the t W rating of the range resistors TABLE l lists the maximum current far any range Theby pass capacitor CI shouldbe ora suitable value topass the a c signal and of appropriate voltage rating TABLE l ...
Страница 18: ... value during balancing will vary the current A large value limiting resistor RL included in series with the supply will keep these variations to a minimum it should be mounted close to the DET VE terminaI to avoid interference pick up The wattage rating of the BALANCE resistors limits the maximum permissible bias current on any range to 40 mA Since the detector is not frequency selective it is ve...
Страница 19: ...d be hwn free and a cap acitor C should be included to by pass any pick up Check or excessive hwn and noise pick up by inserting an open circuit jack plug into the EXT A C socket the meter indication at the sensitivity in use should be negligibly small CAUTION To avoid high transient voltages short circuit Lx before switching off the bias supply 4 This method showninFig 2 11 uses the D C ChokeAdap...
Страница 20: ...n external source or at d c from the internaI battery or an external d c supply Fig 2 12 shows the basic bridge configuration for measurements with a a c and b d c For resistance measurements the LOSS BALANCE arm is replaced by a 100 2 resistor andfor d c measurements the meter only is used as the detector D TECTIM I I l IT I_M T D c S_T IV Wt J 1 a A c b D C Fig 2 12 Basic Resistance Bridges 20 ...
Страница 21: ...sistor should be included in serie s with the bias supply its value being dependent on the volt age used as shown in Table 2 A by pass capacitor of at least l fLF should alBo be included across the jack plug connections to provide a path far the a c signal The bias current is adjusted to bring the test component to the desired working point if necessary reduce the amplitude of the a c until a good...
Страница 22: ...at zero and the SENSITIVITY control fully clockwise The resistance value of the component under test is given by multiply ing the setting of the BALANCE control with the range fun scale as des cribed in Section 2 l 2 6 4 MEASUREMENTS USING AN EXTERNAL D C SOURCE By using an external d c source of higher voltage than the 9 V inter naI battery greater discrimination may be obtained on ranges of lO f...
Страница 23: ... before altering the position of the FUNCTION switch Low Resistance Discrimination on the two lowest ranges may be improved by using the method shown in Fig 2 14 Set the FUNCTION switch to R and con nect a 4 5 V battery to a jack plug inserted into the EXT A C socket A 22alimiting resistor must be included in series with the battery to protect the bridge resistors A sensitive galvanometer connecte...
Страница 24: ...ked to the VE chassis terminaI of the bridge A f f 1AT8 o I EXtAL I SOCI T I I I Fig 2 15 Connection of External A F Source via Isolating T ransformer The TM 7120 transformer has been designed to match an oscillator output impedance of 600 a but may be used far other impedances provided that for lower impedances the input power is limited to t W The lo ad on the secondary will vary from 2 5 a on t...
Страница 25: ...s is 35 V r m s open circuit from a 600 a source This limita the maximwn power into the bridge and test component to W This voltage is more than adequate for ali normal measurements the e m f from the internaI oscillator being 170 mV on the six lowest impedance ranges and 1 5 V on the top two A C Voltage across Inductors With the maximwn y oltage limitations given in the previous paragraph it is p...
Страница 26: ...lair coredcoils are measured in terms ofseriesinductance Lsand seriesresistance Rs withthe LOSS BALANCE at the Q setting 21TiL Here Q Rs High Q coils such as ferrite coredfilter coils are measured in terme of parallel values Lp and Rp on the D x 01 range This is equivalent to a Q range of lO to 00 and far values of Q greater than lO L Ls within 1 With laminated iron cored inductors the predominant...
Страница 27: ...CE potentiometers RV4 and RV5 connected in series or in parallel with it according to the setting of the D Q switch This LOSSBALANCE arm is replaced by a 100 1 resistor R12 far resistance measurements The RANGE resistors associated with switch SB consist of six metal film high stability type R15 to R20 and two wirewound Rl3 and R14 The main BALANCE contrai comprises an eleven step switch SC and a ...
Страница 28: ...istance measurements at the R ffiT D C position of switch SA A source of higher voltage may be connected betweenthe DET VE and VE chassis terminals far better discrimination when the internaI battery is disconnected at the R EXT D C position 3 3 DETECTOR The dètector has been made unselective to enable external a f source s to be used far energizing the bridge its frequency response being sensibly...
Страница 29: ...d output tram the bridge is applied directly to the meter so that now it deflects either side of zero passing through zero at the balance nullo Note Because the detector is unselective pickup of strayfields inaccessories such as the D C Choke Adaptor TM 6113 can result in a standing reading on the meter 1 this problem is not surmountable by moving the bridge and adaptor to another location an osci...
Страница 30: ...re not trapped 4 2 REPLACEMENT OF CIRCUIT COMPONENTS li the precautions and limita described in Section 2 are observed the instrument should not require any maintenance other than the occasionaI replacement of the battery In the event of serious damage however the instrument should be returned to our Service Department or nearest Area office For addresses see rear cover The use of high stabiIity c...
Страница 31: ...circuit jack plug into the EXT A C socket to switch off the internal oscillator alBo check that the internal 9 V battery does not require replacing 4 2 3 OSCILLATOR FREQUENCY The oscillator frequency may be adjusted by padding the value of Cl which is the largest capacitor mounted between the upper tag strips on the left hand side of the instrurnent 4 2 4 RANGE RESISTOR R13 R13 is a loop of resist...
Страница 32: ...091 TP1 HI 23235 176 R34 Carb 3300 1 W 55 C 21 31 2 063 TP2 DET ve 23235 176 TPj Ve ohassia 23235 177 VARIABLB RKSISTORS TRANSISTORS RV1 n 1100 5 5 1 20oC 2582 573 RV2 Caro 2 5k 1 2W 70oC 25673 2 3 VT1 GBT102 281 23 876 RV3 Carb 25k 120 1 70 C RVI n 1700 I W 20oC VT2 OC200 281 33 337 RV5 n 17k 1 20oC 25871 573 VT3 GBT1C2 281 23 876 Rv6 WW 2000 1 W 25886 570 KNOBS SWITCHBS FunctioD 1 111 5 207 SA P...
Страница 33: ...relative to chassis unIess otherwise indicated Measured with a lO kO V meter 3 SYMBOLS preset component arrow indicates cIockwise rotation oI knob panel marking IO o printed board tag number 4 SWITCHES Rotary switches are drawn schematicaIIy Numbers or Ietters indicate contraI knob setting as shown in key diagrams IF 1st section Iront pane1 Iront IB 1st section back lF lnd section Iront etc l700 l...
