Abstract: A gas stream detection apparatus having a balanced resistive bridge network enclosed within a housing and an electronic power supply for driving the bridge network. The power supply includes a voltage source feeding a voltage-to-current converter with two differential inputs, a current sensing resistor between the converter and bridge, twin feedback paths to the differential inputs, and a large source resistance connected to the voltage source and in parallel with a smaller source resistance, each connected to separate differential inputs. The resistance R of two bridge filaments increase by .DELTA.R when exposed to high sample gas concentration causing variations in a current I supplied to the bridge. As .DELTA.R increases, a bridge output voltage E.sub.O decreases. The dependence of current I on .DELTA.R depends on circuit parameters. The difference between the source resistances permits the voltage source to be non-constant and load dependent.

Abstract: A temperature controlled oven apparatus having a central chamber with a heater element and a pivotal inner baffle door, located within a removable outer access door, periodically opened or closed to regulate the exhaust of oven air and the admission of ambient air into the oven through a preheated plenum chamber.