Browse Prior Art Database

Self-Seeking, Autoscaling Measurement Circuit for Instrumentation

IP.com Disclosure Number: IPCOM000060837D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Munoz-Bustamante, C: AUTHOR [+2]

Abstract

This article describes a circuit arrangement which is used to measure voltages or currents for any instrumentation use. The circuit automatically changes detectable range and sensitivity, and has consistent signal-to-noise (S/N) ratio for each scale setting. In traditional autoscaling circuits, the S/N ratio decreases with increased amplifier gain due to multiplication of internal amplifier junction and resistor noise. The measurement system's bandwidth is a function of the amplifier's gain (limits AC measurement capability). The system may not practically be cascaded to a large number of scale changes because of increased parasitic capacitance of additional feedback resistors.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 2

Self-Seeking, Autoscaling Measurement Circuit for Instrumentation

This article describes a circuit arrangement which is used to measure voltages or currents for any instrumentation use. The circuit automatically changes detectable range and sensitivity, and has consistent signal-to-noise (S/N) ratio for each scale setting. In traditional autoscaling circuits, the S/N ratio decreases with increased amplifier gain due to multiplication of internal amplifier junction and resistor noise. The measurement system's bandwidth is a function of the amplifier's gain (limits AC measurement capability). The system may not practically be cascaded to a large number of scale changes because of increased parasitic capacitance of additional feedback resistors. This parasitic capacitance causes the amplifier to roll off in bandwidth, further limiting the ability to measure high frequency AC voltages or currents. The circuit disclosed herein eliminates these problems, by using a low noise amplifier gain stage in the analog measurement section, and achieving autoscaling through changing the sense resistors. This method keeps the S/N ratio of the system independent of the selected sensitivity. The figure is a circuit diagram of the present autoscaling arrangement. At the start of a measurement cycle, the counter 7 receives a clear start signal 1, which resets the counter outputs 4 to '001. The counter outputs 4 feed the demultiplexer (demux) 8 address lines, thus selecting demux outpu...