Subpicoampere current source based on a digital-to-analog converter
A current source based on a voltage ramp generated by a 16-bit digital-to-analog converter and a differentiating capacitor has been developed in MIKES. The system is suitable for generating currents from 1 fA to 100 pA. Standard deviation of average dU/dt:s of 70 ramps during an overnight measurement is as low as 1 ppm.
Vibration Reed Electrometer for Accurate Measurement of Electrical Currents Below 10 pA
The paper is about developing a home-built vibrating reed (VR) electrometer. The heart of the meter is a VR capacitor, which excels in a stable and low input leakage current of only 8 aA with a 2 aA noise for a 1 h measurement. This paper demonstrates that this makes the instrument ideal for the characterization of subtle charge effects in, for example, connectors and cables. The exceptional sensitivity of the electrometer is proven in a measurement of the leakage resistance of an air gap capacitor which results in a value of Rleak = (8.8 0.3) 1017 Omega, obtained at a test voltage of only 10 V. Calibration of the system with both a picoampere and a picocoulomb generator shows that the instrument has an accuracy of 15 parts in 106 (k = 1) at a current of 1 pA. As far as we are aware, this is the best uncertainty for a room temperature electrometer published so far
Palm oil shell aggregate for lightweight concrete
Publisher Summary Increased agricultural production and the development of agro-based industries in many countries of the world have brought about the production of large quantities of agricultural wastes, most of which are not adequately managed and utilized. Low-cost building materials can be produced using inexpensive indigenous raw materials. Agricultural wastes that are renewable and are found in abundance in many countries present an interesting alternative to the traditional and sometimes imported building materials, particularly for low-cost construction. The use of agricultural wastes as aggregates in lightweight concrete can provides an alternative to conventional methods for the production of lightweight concrete. Lightweight concrete results in a reduction in the overall deadweight of a structure and provides a significant saving in the overall cost of construction. The use of less expensive alternative lightweight aggregates in the production of the concrete can provide further reductions in expense. The material properties and structural performance of lightweight concrete with palm oil shells as aggregates are similar to lightweight concrete produced using the more common lightweight aggregates such as clinker, foamed slag, and expanded clay. The palm oil shells are hard and are received as crushed pieces because of the process used to release the oil. Manual sieving is necessary to remove the large amount of fine particles. The shells are then air-dried before use. Because the palm oil shells are lighter than the cement matrix, the shells tend to segregate in wet concrete mixes. On the other hand, dry mixes using palm oil shells are relatively more difficult to work with when compared to ordinary concrete. Trial mixes are necessary to achieve a good mix design.