Test unit for checking the components of the mercury delay line memory system.

The test unit consists of a rack of chassis (corresponding to circuit boards in modern equipment) and is mobile.

(A rack is a metal frame into which modular components (chasses) were bolted. The standard width was 19 inch.)

The test unit generated test signals, which can be controlled by changing frequency and amplitude. The signal could be observed on a cathode ray oscilloscope (CRO). In particular, the receiving and transmitting circuitry of the delay line system was tested.

The testing, involving this unit, was carried out off-line, away from CSIRAC's operating environment; it was used for bench testing. The unit was used to test the delay lines in the main memory and the arithmetic registers.

Some of the equipment in the test unit was designed and constructed in Sydney, being used in the development stage, but not in the operational stage in Melbourne. The technology is a descendant of radar technology.

CSIRAC's memory system used mercury delay lines to store audio pulses.

The memory could accommodate up to 32 acoustic mercury delay lines. (There was actually physical space for 48 but the computer could only access 32 electronically). Each line was a five foot long tube, originally monel metal coated with lacquer (and later stainless steel) and filled with mercury. The mercury filled tubes acted as the medium along which acoustic vibrations passed from a transmitter unit to a receiver unit. These units, known as transducers, consisted of a quartz crystal mounted on a small lead cylinder.

The delay lines were so called because they delayed the data pulses. Pulses travel much slower as acoustic signals than they do in electronic circuitry - the data were thus 'stored' because it took a relatively longer time for the data pulses to travel down the tubes compared to an equivalent 'length' in electronic circuitry. The clock (in Cabinet Front 3, Clock & Sequence Control Circuits) ensured that pulses were 'picked up' at the time they were needed for processing.

The audio pulses were sent down a delay line using a high frequency (HF) 'carrier' wave. The carrier wave was switched on and off to represent '1' and '0'.

There are five chasses and a bottom section in this rack (numbered here only for the sake of clarity):

Chassis Number One (the top chassis ) contains a cathode ray oscilloscope (CRO) to test the receiving pulses

Chassis Number Two (below Chassis Number One) has inputs for receiving signals. It includes a signal attenuator to reduced signals to their appropriate size. It attenuates further the signals form Chassis Number 4.

Chassis Number Three (below Chassis Number Two) is believed to be a pulse amplifier possibly for testing transmitting pulses. Chassis Numbers Three and Five generate and control pulses carried by by the HF signal from Chassis Number Four

Chassis Number Four (below Chassis Number Three) is a test signal generator for testing the receiver transducers in mercury delay lines and possibly the transmitting transducers.
Chassis Number Four has a variable frequency oscillator and an attenuator that produces test signals and reduces their level so they can be used for testing the receiver transducers of the delay lines. They are reduced so they are comparable to the signals actually received in the delay lines during actual operation.
Chassis Number Four tests the frequency range of the memory system, in fact to test whether the response around the mid frequency. In order to represent a digital pulse, there has to be a range of frequencies around the mid frequency of 10 MHz i.e. a bandwidth of a certain range. The receiving amplifier must be responsive to this bandwidth if it is going to pick up the pulse. This is similar to a radio station signal, which occupies a small bandwidth. The frequency and volume of the carrier wave can be changed over the range 5 - 15 MHz.

Chassis Number Five (below Chassis Number Four) tests the ability of the transmitting side of the mercury delay line system to generate pulses. Chassis Numbers Three and Five generate and control pulses carried by the HF signal from Chassis Number Four.

The bottom section contains a filament transformer used to supply the appropriate voltages to valves.

Physical Description

Rectanguar metal cabinet with control chasses in front and no rear covering. There is a probe attached to a socket in chassis #4. See Object Summary for more detail.

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