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### Network # measuring power factor

P

#### Pinchy

Jan 1, 1970
0
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

S

#### Spehro Pefhany

Jan 1, 1970
0
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

Check these out:

http://www.analog.com/library/analogDialogue/bestof/pdf/06_3.pdf

not sure if either is still available...
Thanks for help

(designer has a degree of engineer in elektronics)
Geert

(Maybe designer should learn to use microcontroller)

Best regards,
Spehro Pefhany

J

#### John Fields

Jan 1, 1970
0
I intend to design a device to measure the power factor without the
use of a microcontroller.

---
Why on earth would you want to do that?
---
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

---
Sure.

The single IC is the ROM, a Read-Only-Memory with a cosine lookup
table burned into it.

T

#### Tim Wescott

Jan 1, 1970
0
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:

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.

K

#### Ken Smith

Jan 1, 1970
0
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.

Why are you using such a messy way of doing it?

I suggest:

Run the voltage into an AGC

Run the current into a comparitor.

Use the output of the comparitor to sync. demod. the AGCed voltage.

A

#### Auxiliary User

Jan 1, 1970
0
John said:
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

---
Sure.

The single IC is the ROM, a Read-Only-Memory with a cosine lookup
table burned into it.
New definition of "Single" today, John?

Hello!
Zuzej Maaya

S

#### Spehro Pefhany

Jan 1, 1970
0
John said:
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

---
Sure.

The single IC is the ROM, a Read-Only-Memory with a cosine lookup
table burned into it.
New definition of "Single" today, John?

Hello!
Zuzej Maaya

You could use an ADuC832 or something like that, and get single chip
with the above block diagram, eh?

Best regards,
Spehro Pefhany

P

#### Pooh Bear

Jan 1, 1970
0
Tim said:
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:

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.

Given the loads today on the AC network, It would seem foolish to measure
power factor by the old fashioned phase angle approach.

Your definition is much more appropriate.

Graham

K

#### Ken Smith

Jan 1, 1970
0
John said:
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

---
Sure.

The single IC is the ROM, a Read-Only-Memory with a cosine lookup
table burned into it.
New definition of "Single" today, John?

Use one of the Cygnal micros and you get the ADC the table and the DAC all
in one chip. That would do it.

T

#### The Phantom

Jan 1, 1970
0
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

You haven't told us what accuracy you require.

T

#### Tom Seim

Jan 1, 1970
0
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

Yeah, a Microchip PIC micro w/ADC.

J

#### John Fields

Jan 1, 1970
0
|
Yeah, a Microchip PIC micro w/ADC. >---------------------------------------+

K

#### keith

Jan 1, 1970
0
Because his professor asked the question, and he's been skipping class?

T

#### Tom Seim

Jan 1, 1970
0
He asked if there existed a single IC that can do this, and there is.

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