 Method for mold temperature control |
| What is claimed is: 1. An improved method of controlling the temperature of an injection mold by ... |
|
| Electronic watch with conductor tracks formed on the watch glass |
| In order to overcome these disadvantages, the present invention concerns an analog or digital ... |
|
| Polychromatic photometer |
| What is claimed is: 1. Polychromatic photometer comprising a sample wheel having a plurality of ... |
|
| Absolute spectrophotometer |
| An improved spectrophotometer that has a light source, a scanning type monochromator that has an ... |
|
| Absorbance monitor |
| What is claimed is: 1. A method comprising the step of: focusing light with a mirror from a small ... |
|
| Photometric apparatus with multi-wavelength excitation |
| I claim: 1. Apparatus for providing a source of optical energy to a fluid medium and for measuring ... |
|
| On-line sheet formation characterizing method and device |
| The present invention is directed to a method and device which provide a set of electrical output ... |
|
| Wireless temperature calibration device and method |
| Precise and repeatable calibration of wafer temperature sensors, such as pyrometry, has been a ... |
|
| Lamp-heated chuck for uniform wafer processing |
| Accordingly, the present invention provides a lamp-heated radio-frequency (RF) plasma chuck for ... |
|
|
Hybrid power switch
| Details |
Inventors: Metzler, Albert;
Assignee: International Telephone and Telegraph Corporation (New York, NY)
Primary Examiner: Miller; J D
Assistant Examiner: Salce; Patrick R.
Attorney, Agent or Firm: O'Neil; William T.
A hybrid AC power switching arrangement in which two ganged switch banks in series are employed along with a pair of reverse parallel (back-to-back) SCRs across each contact pair of the second switch gang. SCR control means and interlock control means are provided so that the first switch gang (closest to the power source) closes first, energizing the SCR control and permitting the SCRs to conduct load current in a corresponding phase leg, beginning at or near a zero voltage cross-over point. After all phase legs are conducting through the SCRs, the second switch gang is closed bypassing the SCRs. On circuit break, the second switch gang (i.e., the one closest to the load) is opened first, the load current diverting immediately through the SCRs for another interim period until the SCRs in each individual phase leg are extinguished as the instantaneous current in the corresponding phase lead passes through or near zero. The first switch gang is then opened to completely disconnect from the line to insure against spurious SCR operation thereafter. |
|
DETAILED DESCRIPTION A typical embodiment applying the principles of the present invention will be hereinafter described with reference to a three-phase power system, however, it will be readily understood by those skilled in this art that it could also be applied to single or two-phase arrangements.
The arrangement according to the present invention employs a first gang of switch contact pairs, each pair being intalled in series with a lead corresponding to one of the phases of the source.
A second switch gang comprises two pairs of switch contacts, for interrupting two of the three phase leads of the three phase source, thereby completely interrupting all possible current paths into a delta or star-connected three-wire three phase load.
It will be realized of course, that in the case of a four-wire three phase arrangement (where the fourth wire is a neutral connected to the center of the star or wye) the second switch bank would require three pairs of power switching contacts.
From the foregoing, it will be realized that, in a single-phase system, only one pair of contacts would be required in the first switch and only one in the second switch, both in series with the "hot" line.
In parallel across each switch contact pair constituting a switch element of the second switch gang, is a back-to-back (reverse parallel) pair of solid state devices, preferably of the silicon controlled rectifier type (SCR).
A switch operation delay and interlock arrangement is provided and operates as follows: Assuming the first and second switch gangs are open at the outset, the load and all circuits are de-energized.
To energize the load, the first switch gang is closed.
This energizes the SCR control circuitry and after a brief settle-down time, enables the SCR gates in each phase lead discretely substantially at the time when the instantaneous alternating voltage across each SCR (and therefore across the corresponding second switch gang contact pair with which each back-to-back SCR pair is parallel) passes through zero
|
|
Electrical and Wave 
