Voltmeter design _ Dc Metering Circuits

But how do we c reat e t he nec essary proport ioning

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Unformatted text preview: t ed. But how do we c reat e t he nec essary proport ioning c irc uit ? Well, if our int ent ion is t o allow t his met er movement t o measure a great er volt age t han it does now, what we http://www.allaboutcir cuits.com/vol_1/chpt_8/2.html 1/6 1/22/2014 Voltmeter desig n : Dc M eter ing Cir cuits need is a volt age divider c irc uit t o proport ion t he t ot al measured volt age int o a lesser f rac t ion ac ross t he met er movement 's c onnec t ion point s. Knowing t hat volt age divider c irc uit s are built f rom ser ies resist anc es, we'll c onnec t a resist or in series wit h t he met er movement (using t he movement 's own int ernal resist anc e as t he sec ond resist anc e in t he divider): T he series resist or is c alled a "mult iplier" resist or bec ause it mult iplies t he working range of t he met er movement as it proport ionat ely divides t he measured volt age ac ross it . Det ermining t he required mult iplier resist anc e value is an easy t ask if you're f amiliar wit h series c irc uit analysis. F or example, let 's det ermine t he nec essary mult iplier value t o make t his 1 mA, 500 Ω movement read exac t ly f ull- sc ale at an applied volt age of 10 volt s. T o do t his, we f irst need t o set up an E/I/R t able f or t he t wo series c omponent s: Knowing t hat t he movement will be at f ull- sc ale wit h 1 mA of c urrent going t hrough it , and t hat we want t his t o happen at an applied (t ot al series c irc uit ) volt age of 10 volt s, we c an f ill in t he t able as suc h: T here are a c ouple of ways t o det ermine t he resist anc e value of t he mu...
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