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(20S) Triac Waveforms
10-25-2022, 01:25 PM
Post: #1
(20S) Triac Waveforms
The following calculations involve troide 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 }

Code:
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.
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