## Saturday, December 17, 2022

### HP 20S: Triac Waveforms

HP 20S:   Triac Waveforms

Introduction

The following calculations involve triode AC switches, better known as triacs.  A triac is generally used as a bidirectional power switch device.  James J. Davidson, the original author of the HP 25 programs states "these programs are for use with mean-absolute (also called average) responding voltmeters which are calibrated to read the rms value of a sine wave"  (Davidson, 38).

The variables used in Davidson's programs are:

Vs = root mean square from source

VLMS = root mean square voltage

θ = firing angle of triac in degrees (Davidson, 38)

These programs have been translated to for the use of the HP 20S calculator.

HP 20S Program:  Triac Waveforms

(59 steps)

Given:  Vs and θ°, calculate VLMA and VLMS

Store Vs in R0

Store θ° in R1 (degrees)

Press [ XEQ ] [ A ]

VLMA is displayed

Press [ R/S ], VLMA is displayed

Given:  Vs and VLMA, calculate θ° and VLMS

Store Vs in R0

Store VLMA in R4

Press [ XEQ ] [ B ]

θ° is displayed

Press [ R/S ], VLMA is displayed

Variables:

R0 = Vs

R1 = θ in degrees

R3 = VLMA

R4 = VLMS

Program Code

Key Code:  { Key }

61, 41, A:  { LBL A }

22, 1:  { RCL 1 }

21, 2:  { STO 2 }

24:  { COS }

75:  { + }

1:  { 1 }

74:  { = }

55: { × }

22, 0:  { RCL 0 }

45:  { ÷ }

2:  { 2 }

74:  { = }

21, 3:  { RCL 3 }

26:  { R/S }

51, 41, 1:  { GTO 1 }

61, 26:  { RTN }

61, 41, b:  { LBL B }

33:  { ( }

2:  { 2 }

55:  { × }

22, 3:  { RCL 3 }

45:  { ÷ }

22, 0:  { RCL 0 }

65:  { - }

1:  { 1 }

34:  { ) }

51, 24:  { ACOS }

21, 2:  { STO 2 }

51, 55:  { →DEG }

21, 1:  { STO 1 }

26:  { R/S }

51, 41, 1:  { GTO 1 }

61, 26:  { RTN }

61, 41, 1:  { LBL 1 }

61, 22:  { π }

65:  { - }

22, 2:  { RCL 2 }

75:  { + }

33:  { ( }

2:  { 2 }

55:  { ÷ }

22, 2:  { RCL 2 }

34:  { ) }

23:  { SIN }

45:  { ÷ }

2:  { 2 }

74:  { = }

11:  { √ }

55:  { × }

22, 0:  { RCL 0 }

45:  { ÷ }

61, 22:  { π }

11:  { √ }

74:  { = }

21, 4:  { STO 4 }

61, 26:  { RTN }

Example

Example 1:

Inputs:  θ  = 75° (stored in R1), Vs = 160 (stored in R0)

Results:

VLMA ≈ 100.70552

VLMS ≈ 130.27094

Example 2:

Inputs:  VLMA = 130 (stored in R3), Vs = 160 (stored in R0)

Results:

θ ≈ 51.31781°

VLMS ≈ 149.25534

Source

Davidson, James J.  "Triac Waveforms #1" and "Traic Waveforms #2" 65 Notes V3N10 December 1976.  pg. 38.

All original content copyright, © 2011-2022.  Edward Shore.   Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited.  This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author and any authors of original programs and scripts.

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