Browse Prior Art Database

Current Meter Having Automatic Ranging with Analog and Digital Outputs

IP.com Disclosure Number: IPCOM000085246D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Carbalan, FL: AUTHOR

Abstract

This meter is designed to measure negative DC currents from one microampere full scale to 100 milliamperes full scale with fast response time, and input voltage drop can be trimmed down to less than 100 microvolts on all ranges. It accomplishes this over six ranges in multiples of ten.

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 53% of the total text.

Page 1 of 3

Current Meter Having Automatic Ranging with Analog and Digital Outputs

This meter is designed to measure negative DC currents from one microampere full scale to 100 milliamperes full scale with fast response time, and input voltage drop can be trimmed down to less than 100 microvolts on all ranges. It accomplishes this over six ranges in multiples of ten.

Its primary circuit is a current-to-voltage converter. The converter uses two cascaded operational amplifiers with feedback resistors controlling its range. The analog voltage output of the current-to-voltage converter is available to drive recording instruments. Twelve bits of binary information are also provided to a rear connector to drive data processing equipment.

Range switching is accomplished by a latch driven, binary-code decimal (BCD)-to-decimal decoder/driver. This selects one of the six relays in the resistive feedback circuit of the current-to-voltage converter. The source of BCD code being applied to the latch previously mentioned is controlled by the range switch, which serves to select one of three sources of BCD ranging information.

The switch S1 is wired to provide BCD via switch decks S1A, S1B, S1C, S1D which is manually selected by the user, or to accept BCD inputs from the automatic ranging board or the data input/output connector. Additional functions such as latch enabling selection and start convert selection are provided by decks S1E and S1F.

The automatic ranging circuit board provides the necessary BCD coding to the latch. This is accomplished by a synchronous up/down counter which is controlled by two sensing circuits. One of these circuits senses over-range conditions, the other senses under-range conditions. The counter is then directed to select the appropriate range to provide a midscale reading.

Front panel indicator lights are provided to indicate the meter range selected. Indicator lights are also provided to indicate over-range conditions and the application of an invalid BCD character to the latch. Invalid in this case is designated to mean any BCD input code not of a number between 0 and 5. In this case, no feedback resistor is selected and the input is opened by a protect relay.

The current input is...