Abstract: A combustion control system includes a sensor assembly and a process controller, the sensor assembly including sensors for providing output signals indicative of process variables, the process controller responding to the output signals to maintain a desired operation of the process. The process controller continuously monitors parameters of the sensors and provides alarms whenever any of these parameters deviate from setpoint values, the process controller automatically prioritizing these alarms to provide a display of only the most relevant alarms. A housing enclosing the processor controller provides RFI/EMI shielding of the process controller including the attenuation and absorption of the EMI/RFI energy.

Abstract: A detector for a "Black Box" toll fraud is connected to circuits at the called party's central office and comprises a relay connected in series with the called subscriber's tip (T) lead, a fraudulent call register or indicator, and a normally open time delay switch with a timer actuated by a ringing signal on the ring (R) lead, which switch closes after a predetermined delay interval (ten seconds) to cause energizing of the register. The flow of direct current in the T lead incident to the called party going off-hook energizes the relay and deactivates the switch. The control (C) lead of the central office subscriber circuit is grounded by the off-hook state of the calling party's telephone and is connected to the register by closing of the delay switch, the indication of a fraudulent call being made by the register on removal of ground from the C lead, i.e., when the calling party goes on-hook.

Abstract: A manhole or a catch basin is built up by stacking a number of pre-cast concrete units. The joints between the units are provided, prior to stacking, with a bead of a non-hardening, semi-liquid, mastic waterproof layer to enable subsequent removal of the units without damaging same. The pre-cast concrete unit of this invention is typical by having cutouts in the side wall and corresponding protrusions extending from one face thereof. Hand or tool receiving depressions are provided in one surface of the unit to facilitate the handling of the unit when increasing or reducing the overall height of a manhole. The shape of the unit not only facilitates the production of same but also assists in convenient handling. Due to generally smooth faces, the steaming-off of the waterproof layer prior to the storage of a removed unit is also facilitated.

Abstract: The invention relates to a recuperator having an improved core within the primary heat transfer surface. This core, by its unique construction, achieves a combination of reradiative and convective heat transfer which outperforms either of these separate modes while maintaining a low pressure loss. The core consists of a series of radial plates between which are a series of triangular baffles arranged at an angle with the horizontal of 45.degree. to 70.degree.. The baffles intercept the flow of flue gas and gently channel the flow of gas into a swirling pattern, thereby enhancing convective heat transfer while maintaining low pressure loss. The staggered triangular baffles also tend to reflect radiation that would otherwise be lost back to the primary heat transfer surface.