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ELECTRONIC 

WATTMETER 

EW604 

1160–00604 

 

 

 

 
 
 
 
 
 
 
 
 
 
 

 

 

 

 

 

 

Feedback Instruments Ltd, Park Road, Crowborough, E. Sussex, TN6 2QX, UK. 

Telephone: +44 (0) 1892 653322,      Fax: +44 (0) 1892 663719. 

email: [email protected]     website: http://www.feedback-instruments.com

 

Manual: EW604  

 Ed01-1    122013

 

Feedback Part No. 1160–00604 

Summary of Contents for EW604

Page 1: ...ck Instruments Ltd Park Road Crowborough E Sussex TN6 2QX UK Telephone 44 0 1892 653322 Fax 44 0 1892 663719 email feedback feedback instruments com website http www feedback instruments com Manual EW604 Ed01 1 122013 Feedback Part No 1160 00604 ...

Page 2: ... under the supervision of a suitably qualified and experienced person in a laboratory environment where safety precautions and good engineering practices are applied By the nature of its intrinsic teaching functionality parts are visible and accessible that might normally be covered up or encased in an industrial or domestic product For this reason students attention should be drawn to the need to...

Page 3: ...g the safe disposal of electronic and electrical items and not placed with ordinary domestic or industrial waste Product Improvements We maintain a policy of continuous product improvement by incorporating the latest developments and components into our equipment even up to the time of dispatch All major changes are incorporated into up dated editions of our manuals and this manual was believed to...

Page 4: ...or otherwise without the prior permission of Feedback Instruments Limited ACKNOWLEDGEMENTS Feedback Instruments Ltd acknowledge all trademarks MICROSOFT WINDOWS 8 WINDOWS 7 WINDOWS VISTA WINDOWS XP WINDOWS 2000 WINDOWS ME WINDOWS NT WINDOWS 98 WINDOWS 95 and Internet Explorer are registered trademarks of Microsoft Corporation MATLAB is a registered trademark of Mathworks Inc LabVIEW is a registere...

Page 5: ...ity to radiated radio frequency fields in order to comply with the EMC Directive In all other respects the specification and operating instructions for the EW604 and EW1604 are the same The only other difference is that the protective fuse in the input lines not the mains fuse has been moved from the rear to the front panel ...

Page 6: ...vi ...

Page 7: ...04 to circuit under test 2 6 Measuring power in a three phase system 2 7 Measuring systems with low power factor 2 8 Amplifier power measurement 2 9 Measuring power in audio frequency circuits 2 10 Audio frequency power comparison 2 11 Measuring radio frequency power CHAPTER 3 Circuit Description 3 1 Multiplying circuit 3 2 Overload circuits 3 3 Power supply circuit CHAPTER 4 Maintenance 4 1 Acces...

Page 8: ...METER AMPS O S C POWER q REV j Hi SET ZERO FEEDBACK ELECTRONIC WATTMETER EWS04 Fig 1 1 Electronic Wattmeter 4 Electronic Wattmeter VOLTS 0 L so 100 ...

Page 9: ...l precautions are taken to prevent damage to the instrument in the event of gross overload of current or voltage Pushbuttons enable the meter deflection to be reversed to measure reverse power flows and also to increase the meter sensitivity by x2 to improve readability of small deflections The wattmeter contains its own partly regulated power supply for operation on normal line voltages The value...

Page 10: ...n power switch Separate green power ON indicator Current Eight position rotary range selector Voltage Eight position rotary range selector Terminals Four 4mm red socket binding posts two for connection to supply and two for connection to the load with mimic showing metering circuits Meter Mirror scale moving coil meter calibrated in watts Zero separate knob for electrical meter zero x2 Pushbutton ...

Page 11: ... range Frequency range DC to 20kHz All voltage ranges 5kQ Volt All current ranges less than 60mQ 3 1 4 mirror scale graduated 0 to 1 0 in 50 divisions Reading given by Watts meter deflection x Voltage range x Current range Pushbutton to give x2 scale expansion and pushbutton meter reversal Many factors control the final indication on any wattmeter They include voltage current and power ranges powe...

Page 12: ... on a single batch of instruments 3 Guaranteed figures are from measurements made on every instrument Fig 1 2 shows the area of operation within which the EW604 may be expected to give results accurate to better than 5 of fsd and should be interpreted in conjunction with the accuracy figures given for the calibration frequency of 50Hz Area of operation 10 50 100 1k 10k 20k Calibration Frequency Fr...

Page 13: ...Dimensions and Weight Width Depth Height with feet Weight 9 330mm 13in 238mm 9 4in 118mm 4 6in 1 9kg 4 31b Electronic Wattmeter Chapter 1 ...

Page 14: ...Electronic Wattmeter NOTES 10 ...

Page 15: ... board Set the switch to 115 for operation from 100 to 125V and to 230 for 200 to 250V 50 60Hz AC The colour code of the power supply cable is Brown Blue Green Yellow Live Neutral Ground The ground wire is connected to the graphite screening of the case but is isolated from the front panel common terminal The current and voltage ranges should be selected to suit the current voltage present in the ...

Page 16: ...0 400 1k 2k 25 50 100 250 500 1k 2 5k 5k 50 100 200 500 1k 2k 5k 10k Fig 2 1 It is recommended that the lower front panel COMMON terminals are operated at neutral potential and in no case at a potential exceeding 400V d c or peak and the upper terminals at no more than 1500V d c or peak with respect to the normal supply ground green yellow wire in the supply cable to the rear of the EW604 The EW60...

Page 17: ...rrent coils or the voltage coils in the power supply measured With the EW604 connected as in fig 2 3 a the power consumed by the voltage circuit at 5000 ohms V is so small that it is insignificant compared with load power This enables the prearranged connections as shown on the front panel schematic to be used without need for correction However the EW604 may if desired be connected as in fig 2 3 ...

Page 18: ... on the supply or a star point on the load the power can be measured by connecting as in fig 2 4 and multiplying the reading obtained by three EW604 3 phase supply 8 _ y L a Supply neutral available 3 phase JRB supply ty b Star point of load available Fig 2 4 Finding the power in a balanced load system If the supply and load are balanced both the power and the power factor can be obtained from two...

Page 19: ...he voltage connection is taken to that one in each case Connections are shown in fig 2 6 for three wire and four wire three phase systems If only one wattmeter is available it may be connected in each of the positions shown in turn The power is the sum of all the readings This scheme of connections can be extended to any number of wires taking n 1 readings in the n wire case Also it is not in prin...

Page 20: ...ery small deflection corresponding to a small iron loss This difficulty may be overcome by the use of power factor correction capacitors In theory the use of such capacitors to tune the transformer inductance does not affect the power reading but it does reduce the supply current enabling a more sensitive current range to be used without overloading the wattmeter thereby providing a more significa...

Page 21: ...ed to the terminals labelled LOAD and the dummy load or loudspeaker connected to the terminals labelled SUPPLY as in fig 2 8 If possible connect the wattmeter common to the amplifier common or ground In this way any power consumed by the current measuring circuit as well as that in the load is indicated on the wattmeter giving a more accurate reading Also the direct connection between the amplifie...

Page 22: ...s Watts rms If it is assumed that Watts rms has the same meaning in relation to watts as volts rms does to volts then Watts rms means the Square root of the mean value of the square of the instantaneous watts It is by no means certain that this is always intended when watts rms is used It may sometimes be employed to denote real power as opposed to reactive or imaginary power but as such is a misn...

Page 23: ...Comparison Electronic Wattmeter Chapter 2 Wrms 1 1 1 225 if 1 342 if 1 414 J2 In the audio range of frequencies power measurement comparisons between two systems having values P1 and P2 can be expressed logarithmically in terms of the decibel dB being one tenth of a bel The expression then is p2 dB 10 log 10 p1 The standard reference unit for P1 is 1 milliwatt of power in a 600 ohm resistive load ...

Page 24: ...of the grease spot photometer adjusted so that the illumination of lamp L1 radio frequency load equals L2 When this occurs the grease spot disappears The switch is then set to position 2 and the autotransformer adjusted till the grease spot again disappears When this occurs the EW604 gives the same indication as the power output from the radio frequency source Amps Voltse 00 u supply Reference lam...

Page 25: ...rrent input The basic multiplying circuit is shown in fig 3 1 while the full circuit is shown in the Maintenance Chapter as fig 4 3 Transistors TR1 to TR5 are a matched array All the emitters are at virtual earth points and all the base currents are supplied by operational amplifiers AC or AA The output product is the difference between collector currents at A and B These points are again held at ...

Page 26: ... illuminating the overload indicator The current circuit is protected against excessive inputs by the 1OA slow blow fuse Diodes 01 and 02 protect the input of AC from excessive voltages until the fuse ruptures With the voltage input TR6 and TR7 detect voltage excursions outside the linear range and illuminate the overload indicator via TR8 Excessive input voltages cause the emitter base junction o...

Page 27: ...onnections to the power transformer EVERY PART OF THE MAINS CIRCUIT CAN CARRY DANGEROUS VOLTAGE WHILE THE POWER CABLE IS CONNECTED AVOID ALL CONTACT The wattmeter has been designed to allow access to all the components by removal of the case First remove the handle by pulling it outwards at each end in turn thereby releasing each centre cap see fig 4 1 This needs firm pressure Then remove with a P...

Page 28: ...readjustment of the various trimming controls on the PC board The Alignment Schedule should be consulted If any of the preset trimmers is widely out of adjustment the possibility that a fault condition is occurring should be considered The table in fig 4 4 indicates the most probable area of such a fault corresponding with each trimmer Trimmer Possible area at fault R22 Current Offset AC R35 Linea...

Page 29: ... not a fault finding procedure An oscilloscope and a chopped source of alternating DC as in fig 4 6 can be used Some reference for setting the final calibration should also be available preferably a dynamometer wattmeter of known accuracy Remove the top and bottom covers of the case and place the instrument upside down so that the various trimmers are accessible Connect the oscilloscope Y input to...

Page 30: ...onvenient to switch faster than 20Hz as this will provide a more persistent oscilloscope display The adjustment sequence is as follows set VOLTS range to 10 then 1 Close SWv turn AMP switch to 10 adjust BALANCE VOLTAGE R44 to bring the square wave display to minimum zero amplitude 2 With SWv still closed turn AMP switch to 05 adjust CURRENT OFFSET R22 to again minimise the amplitude of the display...

Page 31: ...SWv and close SWA adjust BALANCE CURRENT R33 to minimise square wave this may result in a waveform sequence as in fig 4 8 4 With SWA still closed adjust LINEARITY R35 to remove remaining pedestals as in fig 4 9 r or or Figs 4 8 or to Fig 4 9 5 Change the scope sensitivity to 0 02V div Keep SWA closed and close SWv adjust R44 to bring both steps equal as in fig 4 i 0 r r r Fig4 10 27 ...

Page 32: ...eter FIG 4 11 Su1table dummy load This connection of the EW604 to a standard wattmeter as shown in fig 4 11 enables a direct comparison of sensitivities to be made without the need for corrections due to internal power consumption Select suitable compatible ranges and use R42 and R21 in turn to bring the deflection of the EW604 to the same value as the standard wattmeter Note that it will be neces...

Page 33: ... R22 33 35 42 44 0 1W 20 16mm body dia R21 4mm shaft dia 7mm bush 25V 50 25 see PWB C1 2 5 35V see PWB C3 4 r 1 16 2 I I I C G I I I I I 1014 II I 0 2 5 1 Fig 4 12 If the Ferranti transistor types are not available the following types bearing EIA or Pro Electron type numbers may be used This table does not imply that the types listed are equivalents in any other situation Ferranti EIA Pro Electron...

Page 34: ...h Feedback Instruments Ltd Crowborough Sussex Should the instrument be returned for repair and recalibration at any time the mains plug should be removed as no provision for the plug is included in the packing when we return the instrument to you The address to which an instrument should be returned is Feedback Instruments Limited Servicing Department Park Road Crowborough TN6 2QR Sussex England 3...

Page 35: ...9 81 e TR11 0 TRB r l_ i1 R46s R41 35 R2 RJ R4 RS R44 ACir Ji 3 C2 17 51 51 51 D1 Ji24 0 0 R31s 1 R23 1 1 M C1 e R13 l1 0 0 R47 0 12 71 0 T1 I 1 5 11 010 011 Im C3 21 1 R49 06 fJI J 1iLF AD R27 FEEDBACK oo R30 j f AE f1l PWB 1 604 B2GOA ISS 5 El R34 1 f R39 f I f R42 AF f LK7 f fl I R43 2 zs 2S 21 0 DO 0 0 0 31 0 0 FS2 31SrnA 11 0 0 R51 ORSO 9 9 Q99 n6W3 SW4 U45 0 0 DDDDDDDD 1 2 3 4 5 6 1 8 B260C ...

Page 36: ...Electronic Wattmeter Chapter 4 J Fig 4 3 Circuit Diagram Drg No 2 604 8269 Iss 5 32 ...

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