Browse Prior Art Database

Isolated Fail Safe Analog Output Circuit

IP.com Disclosure Number: IPCOM000094719D
Original Publication Date: 1965-May-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Sinnott, JF: AUTHOR

Abstract

When a digital computer is used in a process control environment, there is a need for circuitry which allows the digital computer to control the magnitude of the current through a particular load. Circuitry must be provided that accepts pulses from the computer and changes the output current in response to these pulses. Between the pulses from the computer, the output current must remain constant at the previously established value. The circuit must also allow the computer to sense the magnitude of the current through the load.

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 68% of the total text.

Page 1 of 2

Isolated Fail Safe Analog Output Circuit

When a digital computer is used in a process control environment, there is a need for circuitry which allows the digital computer to control the magnitude of the current through a particular load. Circuitry must be provided that accepts pulses from the computer and changes the output current in response to these pulses. Between the pulses from the computer, the output current must remain constant at the previously established value. The circuit must also allow the computer to sense the magnitude of the current through the load.

In this circuit, the computer regulates the current flowing from power supply PC to load RL. The computer applies control pulses to terminals C and D to control the current flowing to RL. The computer can sense the current applied to RL through terminals E and F.

Transistor T1, the amplifier 10 and the associated bridge circuit that includes R1...R4 forms a current regulator circuit. Changes in output current are detected and amplified by amplifier 10, thus, changing the state of T1 and maintaining the current in the load constant.

Device 12, an ampere hour meter manufactured by Curtis Instruments, Inc., forms one arm of the bridge circuit. It consists of capillary tube 12A filled with mercury which has a gap, light source 12B, photoresistor 12C and two masks 12D and 12E. By applying current to terminals C and D, the resistance of 12C is changed. Changing the resistance of resistor 12C changes the b...