A large rack-mounted electrical instrument finished in two tones of grey. There are two prominent meal handles at either side of the front face, and a CRT display at its centre. The sides and top are perforated with small ventilation holes. Two spring-loaded handles fold into recesses at either side of the instrument.
The back of the instrument has a power cord and a series of jacks and terminals.
Accession Number: 2024.ph.884
Alternative Name:
Primary Materials: Iron Alloy, Plastic
“Geophysics Dept. U of Toronto” is scratches into the top of the front console.
Manufacturer’s Labels at the back of the instrument include the following information: “SPECIFICATION OPTN 020”; [Serial Number] “1405U00533”
Dimensions (cm): Height = 27, Width = 43, Length =44 .
The correlator is a digital signal processing instrument for filtering noise from data by “correlating” two signals in real time. The instrument compares two signal waveforms by sampling them at regular intervals, multiplying the respective samples together, and adding the products. Samples that are correlated will have large products. Less correlated signals will have smaller products, and completely uncorrelated signals will average to zero when sampled over time.
This principle has a variety of technical applications including noise filtration, signal direction finding, and the measurement of absorption coefficients influencing a return signal.
The correlator processes up to 100 samples at a time. These are displayed in real time on the CRT display screen.
Samples can be time-shifted to account for the delay of a return signal.
This instrument has minor signs of wear such as scratches, scuffs, and small patches of dried adhesive. The outer layer of the removable power cord has become slightly tacky.
Associated Instruments:
Hewlett Packard Great Britain, South Queensferry, Scotland
Date of Manufacture: c. 1969 – 1979
This artifact is part of a small collection gathered from the office of Prof. Nigel Edwards of the University of Toronto Department of Physics in March of 2022.
This example was purchased for the electromagnetic sounding experiment described in Duncan et al. 1980. It was not used in any subsequent experiments.
Hugh Walker (2021) “The Definitive History of Hewlett-Packard South Queensferry, Scotland.” (archived Feb 22, 2024). This privately published three-volume memoir, created by the HP Memory Project, provides a detailed account of the Scottish center at which the Correlator was designed.
George C. Anderson and Michael A. Perry (1969) “A Calibrated Real-Time Correlator/Averager/Probability Analyzer.” HP Journal, November 1969. 9-16. (archived Feb 25, 2024).
P. M. Duncan, A Hwang, R. N Edwards, R. C Bailey, and G. D Garland (1980) “The Development and Applications of a Wide Band Electromagnetic Sounding System Using a Pseudo-Noise Source.” Geophysics 45, no. 8 (1980): 1276–96.
The correlator began development in 1967 at the recently founded Hewlett-Packard South Queensferry plant west of Edinburgh, Scotland. It was developed to complement the Noise Generator (3722A), primarily for testing and developing control systems. It simplified laborious calculations previously performed on digital or analogue computers.
The system represents an early use of logic ICs. The correlator was produced between 1969 and 1979 and sold 610 units (see Walker 2021).
This example was purchased as part of the apparatus used in the electromagnetic prospecting experiment described in Duncan et al. 1980. This involved a pseudo random time-domain electrical signal sent through a bipole transmitter and received through either an air-core coil or a Scintrex MFM-3 High Sensitivity Vector Fluxgate Magnetometer depending on the selected frequency. The correlator was used to produce autocorrelograms and crosscorrelograms comparing the transmitted pseudorandom binary sequence (PRBS) signal with the voltage analogue of the received magnetic field.
Large scale trials were carried out in 1976 and 1977 near Timmins, Ontario using a transmitter wire 20.5 km in length.