LAUGHTON ELECTRONICS |
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Cooked: an environmental test chamber |
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| Here I describe a device built, by customer request, to interconnect with existing equipment in a Product Test Lab. | |
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An international manufacturer of automotive rubber products contacted me in regard to some equipment used in one of their product testing laboratories. The laboratory had a mandate for destructive and non-destructive testing. Unfortunately, conditions in the lab were harsh, and occasionally it was the test equipment that got destroyed! In this case an accident had damaged a chassis with electronic controls used to regulate temperature in a test chamber. The damaged chassis had been discarded, and I was asked to build a replacement. the test apparatusThe products being tested were automobile engine mounts of rubber and steel construction, and at the heart of the test apparatus was a chamber in which the engine mounts would be stressed — both thermally and mechanically. The test chamber, somewhat comically, resembled a bar fridge. However, the door had a window in it, and all the interior and exterior surfaces were stainless steel. A sturdy metal column projected up through a hole in the floor of the chamber, and another came down through the top; the columns were used to attach the Device Under Test to an external system that applied the desired mechanical loading. The chamber was heated by a high wattage 230 volt element; connections for it and some other devices were brought out on a military style connector on the outside wall of the chamber. the custom built controlsEverything beyond the connector was replaced. A heavy flexible cable ran from the remotely located chassis. The cable included a heavy gauge safety ground and heater connections, as well as conductors to power the chamber's 230 volt circulation fan. The chamber also had a small 115 volt lamp included as an aid in viewing the tests. (Interestingly, the chamber had at one time also been equipped for refrigeration, simply using a solenoid valve to vent gas from a high-pressure cylinder and relying on the gas's expansion for cooling. But I was told refrigeration wouldn't be required, so this feature wasn't accommodated by the new control chassis.) Temperature in the chamber was sensed by a thermocouple, and (using wire and connectors of the appropriate alloy) the thermocouple signal got routed from the chamber back to the chassis and to a PID controller module. The controller output activated a solid state relay which in turn switched power to the 230 volt heater. Completing the assembly were a double-pole main breaker, a small step-down transformer to supply the 115 volt bulb, and various switches, pilot lights and low-amperage fuses for the lamp and control circuits. |
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