Pinchy said:

I intend to design a device to measure the power factor without the

use of a microcontroller. In the design, the measured angle will be

given by a simple DC voltage, e.g. 30° = pi/6 rad = 0.523 V

A problem that occurs is calculating the cosine of this voltage. In a

discrete setup, I will use Taylor series and realise it with analog

multipliers and a few operational amplifiers.

Before starting this, I would like to know if a single IC exists that

can make this calculation at once, eg 0.523 V IN results in cos(0.523)

= 0.866 V OUT

Thanks for help

(designer has a degree of engineer in elektronics)

Geert

Power factor can either be defined as pf = cos(theta_v - theta_i), where

theta_v and theta_i are the phases of the voltage and current,

respectively, and we assume that all waveforms are pure sinusoids.

I better definition in my mind is the one that goes:

Power to Load

pf = -----------------.

(V_rms)*(I_rms)

This definition accommodates all sorts of situations where the "pure

sinusoid" definition doesn't, like pulsed currents (even on a DC line),

harmonic currents from rectification, or anything else you can dream up.

If you are not bent on measuring the sign of the reactive vars, then you

can build your power factor meter with a couple of RMS chips and a few

multipliers, all from ADI.

And you won't have to mess with trig functions.