Background: Each particle of dust in the air flowing in a duct carries with it a minute triboelectrical charge. A probe in the duct collects the charge from the particles which impinge upon it. The resulting electric current, which is measured in femtoamps (1/1000000000000000 amp), can be used to detect and measure the amount of dust hitting the probe. This capability is used to monitor the condition of air filters and in process control applications.

Project: Product Resources worked with the founders of a start-up company to help develop their new product line. The ultra sensitive amplifiers required were designed and developed to the customer's specification in Product Resources' Wakefield laboratory. On its most sensitive scale, this amplifier is capable of detecting a current that corresponds to only 150 electrons per millisecond! It is interesting to note that, at these current levels, the electrical leakage of printed circuit board laminate becomes a design factor, and a fingerprint in the wrong place can cause a major calibration error. Product Resources engineers designed into the amplifier an integrated test feature which enables correct operation of the entire circuit to be verified. The output of the instrument is a warning signal if the particle flow rate exceeds a preset limit, a digital LCD flow meter display, and a 4-20 mA signal for process control.

Technologies: ultra low current amplifiers, low noise analog circuits, intrinsically safe (energy limited) circuit design, precision sheetmetal work

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