ZF2/ZF3 SCR Power Controller
Theory
Rev 3
Ametek HDR Power Systems
21
CHAPTER 6 - Theory
6.1
Functional Description
The main function of the ZF2/ZF3 is to control the amount of power delivered to a load.
The SCR is either on or off and conducts in one direction when turned on. Because the SCR only
conducts in one direction, two SCR’s are connected in “inverse parallel” configuration, Figure 6.1. A
small gate signal is applied to turn on the SCR. Once the SCR is turned on, it will remain On until the
current through the SCR goes below the holding current level.
Figure 6.1 AC Switch
6.2
Digital Firing Control Circuit
Firing (gating) of the SCRs is controlled by a digital firing control circuit synchronized to the line
frequency (50 or 60 Hz). The firing control circuit may be manually controlled by the built-in ZERO
control or a remote potentiometer. Automatic control may be from a temperature or process controller
that provides a demand-proportional low-level voltage or milliampere output signal. The firing control
circuit may also be turned on and off by an external switch or relay contacts. (Chapter 4 discusses
some external control methods.)
6.3
Variable-Time Base
The firing control circuit of the ZF2/ZF3 operates on a variable rather than fixed time base. Operating
on a fixed-time base of 1/3 second (20 cycles), for example, at 50% power the SCRs would be on for
10 cycles, off for 10 cycles, on for 10 cycles, and so on. Operating on a variable-time-base, at 50%
power, the SCRs are on for one cycle and off for the next. At 75% power, the controller, with a fixed-
time-base of one-third second (20 cycles), would be on for 15 cycles and off for 5. The variable-time-
base, however, would be on for three cycles, off for one, and so on. The time required to describe the
operation of the ZF2/ZF3 would be the period of four cycles in this case – three cycles on and one
cycle off.
Table 6.1 Variable-Time-Base Relationship (Example)
Control signal, %
Power Demand
SCR Pair, Complete
On Cycles
SCR Pair, Complete
Off Cycles
1%
1
99
25%
1
3
50%
1
1
60%
3
2
70%
7
3
75%
3
1
80%
4
1
90%
9
1
95%
19
1
99%
99
1
100%
ALL
0
Содержание ZF2 SCR Series
Страница 6: ...Table of Contents ZF2 ZF3 SCR Power Controller iv Ametek HDR Power Systems Rev 3...
Страница 8: ...Safety Instructions ZF2 ZF3 SCR Power Controller 2 Ametek HDR Power Systems Rev 3...
Страница 23: ...ZF2 ZF3 SCR Power Controller Operation Rev 3 Ametek HDR Power Systems 17 Figure 4 9 Unbalance Block Diagram...
Страница 24: ...Operation ZF2 ZF3 SCR Power Controller 18 Ametek HDR Power Systems Rev 3...
Страница 32: ...Troubleshooting ZF2 ZF3 SCR Power Controller 26 Ametek HDR Power Systems Rev 3...
Страница 42: ...Appendix ZF2 ZF3 SCR Power Controller 36 Ametek HDR Power Systems Rev 3 Appendix C ZF2 60 225 A Outline R...
Страница 43: ...ZF2 ZF3 SCR Power Controller Appendix Rev 3 Ametek HDR Power Systems 37 Appendix D ZF2 350 500 A Outline R...
Страница 44: ...Appendix ZF2 ZF3 SCR Power Controller 38 Ametek HDR Power Systems Rev 3 Appendix E ZF2 650 A Outline R...
Страница 45: ...ZF2 ZF3 SCR Power Controller Appendix Rev 3 Ametek HDR Power Systems 39 Appendix F ZF2 800 1200 A Outline R...
Страница 46: ...Appendix ZF2 ZF3 SCR Power Controller 40 Ametek HDR Power Systems Rev 3 Appendix G ZF3 60 225 A Outline R...
Страница 47: ...ZF2 ZF3 SCR Power Controller Appendix Rev 3 Ametek HDR Power Systems 41 Appendix H ZF3 350 500 A Outline R...
Страница 48: ...Appendix ZF2 ZF3 SCR Power Controller 42 Ametek HDR Power Systems Rev 3 Appendix I ZF3 650 A Outline...
Страница 49: ...ZF2 ZF3 SCR Power Controller Appendix Rev 3 Ametek HDR Power Systems 43 Appendix J ZF3 800 1200 A Outline R...
Страница 51: ...Notes...
Страница 52: ...503 Lakeview Plaza Blvd Ste C Worthington Ohio 43085 USA...
