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Ask The Search Engineer

Ask The Search Engineer

Dear Search Engineer: Any idea where I can find Brinell, Vickers, and Rockwell hardness conversion tables for ductile cast iron?-G.D. in London

Dear G.D.: They don't call me the Search Engineer for nothing! I did a Google(R) search and came up with the perfect site for you, direct from the There are tables and tests for all the requested information and more. Bookmark the site, old chap!

Dear Mr. Search Engineer: If I subtract two-phase coherent signals that have random white noise (each signal having the same RMS noise) and measure the standard deviation, do I need to divide the result by the square root of two to get the true standard deviation or RMS noise? I need to do something like this to remove fixed pattern noise and dc offset from a video signal to be able to measure purely random noise.-V.K. in MA

Dear V.K.: If the white noise in the signals is independent, you need to multiply the standard deviation by 1.414. If the signals in each channel are 180 degrees out of phase, you will get twice the signal level of a single channel. The net result is two times the signal and 1.414 times the noise for a net gain in SNR of 1.414 (3 dB). If the signals in each channel are in-phase, you will get no signal and 1.414 times the noise of a single channel.

Dear Mr. Search Engineer: I'm looking for any high-temperature compatible adhesive that can be used to adhere a thermocouple to a crucible at temperatures of 2,000C.-R.S. in OH

Dear R.S.: Sorry, but at the temperature you indicated, thermocouple materials melt. The answer is to use an indirect infrared-type readout if you need to have a view of the object. I'd suggest that you try to wedge the thermocouple into or onto the crucible.

Dear Search Engineer: I'm looking for a simple and relatively low cost method of installing flexible plastic hinges between 12 x 24-inch sheets of 1/8-inch thick polypropylene or polythylene. Hinge rotation is 180 degrees allowing the adjacent sheets to fold back and stack in contact face-to-face. Hinges need to be flexible and last approximately 3,000 cycles. I'm interested in methods of producing such hinges (either formed into single 24 x 24-inch sheets to produce two hinges between 12 x 24-inch sheets, or separately attached hinges to two 12 x 24-inch sheets).-G.D. in IL

Dear G.D.: You can mechanically coin a hinge into a sheet of PP or PE. Nip press must have 1/8 inch radius on one side, flat on the other, thickness reduction ratio at the pinch should be about 4:1. Of course, the other option you could consider would be to run an extruded hinge in PP and weld it to PP sheet.

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