This article was originally published in Electrochemical and Metallurgical Industry Publication of May 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.
When pyrometers were first transferred from the laboratories to the works they were used in the same forms, exactly, as when in the laboratories, yet they received quite different treatment and were desired for somewhat different use. One step after another has been made to make the works instruments suitable to industrial requirements.
By far the majority of high temperature processes employ temperatures between 200° and 1,000° C and it is fortunate that thermocouples of certain metals and alloys give us stable and comparatively heavy currents within that range. By keeping down the resistance of the thermocouple; the lead and the measuring instrument, sufficient current is obtained to move the system of a double pivoted galvanometer. This means a portable or wall pattern galvanometer that can be handled as one would handle a voltmeter or ammeter, that is not affected by vibrations, and that is not expensive.
Hand in hand with the robust galvanometer comes the non-fragile portion of the pyrometer that is to go into the furnace. Either two thermocouple elements, in the form of heavy rods or one in the form of an outer-tube and the other a rod inside and insulated from it make up the furnace piece. Retaining each and all of these improvements in the works pyrometer the new industrial pyrometer, just being put out by the Wilson-Maeulen Co. New York City, has the great added advantage of being easy to read.
A glance at the indicator shows the general appearance of it, but to realize how easy it is to read this instrument at a distance from it it must be borne in mind that the dial is 10 inches across. The scale is actually 7 ¾ inches long and graduations so large that it can easily be read 12 feet away. And this is a real advantage and not only an apparent one, for we all know how much oftener things that are easy to do are done than are those which are not. When the men in the works have a great big finger continually pointing at the temperature they are forced to see and respect it. It practically forces itself upon them. When a man has to leave his work and go over and squint at an indicator he will do it just as seldom as he thinks he may. When it is so big that he can read it 12 feet away he feels that he has something to help him, not that it is an intruder that is brought in to take up his time, introduce complications and give him trouble to use.
In this industrial pyrometer the thermocouple is in the form of a pure iron tube as one element of the couple, the other element being a rod of special alloy which passes down through the tube, being insulated from it at all points. The tube is closed at one end and at that point the tube and rod are electrically welded.
This thermocouple makes a particularly strong fire-rod which stands an enormous amount of abuse for the reason that the insulation separating the two elements is inside the tube forming one element and so is not subjected to abrasion. In most cases the fire-rod needs no auxiliary protection, and so being exposed directly to the heat quickly assumes the surrounding temperature, causing the indicator to respond quickly to temperature changes.
The highly polished brass case with beveled plate glass front make this industrial pyrometer an exceedingly attractive instrument. The pivoting of the moving coil in jewel bearings ensures lasting sensitiveness, a requisite for continued accuracy.
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