Voltmeter design _ Dc Metering Circuits

Eac h resist or is sized t o provide a part ic ular f

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Unformatted text preview: no resist or at all, providing an "of f " set t ing. Eac h resist or is sized t o provide a part ic ular f ull- sc ale range f or t he volt met er, all based on t he part ic ular rat ing of t he met er movement (1 mA, 500 Ω). T he end result is a volt met er wit h f our dif f erent f ull- sc ale ranges of measurement . Of c ourse, in order t o make t his work sensibly, t he met er movement 's sc ale must be equipped wit h labels appropriat e f or eac h range. Wit h suc h a met er design, eac h resist or value is det ermined by t he same t ec hnique, using a known t ot al volt age, movement f ull- sc ale def lec t ion rat ing, and movement resist anc e. F or a volt met er wit h ranges of 1 volt , 10 volt s, 100 volt s, and 1000 volt s, t he mult iplier resist anc es would be as f ollows: http://www.allaboutcir cuits.com/vol_1/chpt_8/2.html 4/6 1/22/2014 Voltmeter desig n : Dc M eter ing Cir cuits Not e t he mult iplier resist or values used f or t hese ranges, and how odd t hey are. It is highly unlikely t hat a 999.5 kΩ prec ision resist or will ever be f ound in a part s bin, so volt met er designers of t en opt f or a variat ion of t he above design whic h uses more c ommon resist or values: Wit h eac h suc c essively higher volt age range, more mult iplier resist ors are pressed int o servic e by t he selec t or swit c h, making t heir series resist anc es add f or t he nec essary t ot al. F or example, wit h t he range selec t or swit c h set t o t he 1000 volt posit ion, we need a t ot al mult iplier resist anc e value of 999.5 kΩ. Wit h t his met er design, t hat 's exac t ly what we'll get : RTota l = R4 +...
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