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
VLMA = average load 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
R2 = θ in radians
R3 = VLMA
R4 = VLMS
Program Code
Key Code: { Key }
61, 41, A: { LBL A }
61, 24: { RAD }
22, 1: { RCL 1 }
61, 55: { →RAD }
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 }
61, 24: { RAD }
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.
