Digital Cannon Tester (1972)
The so-called Royal Netherlands Navy Guided Weapon (GW) frigates Tromp (F801) and De Ruyter (F806), with the characteristic large radar dome, would be equipped with a 12-cm Bofors cannon. These cannons came from the submarine hunter Gelderland and date back to the 1950s. The 1973 new class of frigates were also equipped with digital fire control.
The control of the cannon had to be powerful enough to be able to transmit the desired control signal and care for the stabilisation for ship movements. The result of the inaccuracies in the digital fire control system and the digital control circuitry, noise is created, which also demands part of the control power.
HSA (Hollandse Signaal Apparaten) suggested performing the calculation of azimuth and elevation angles at a frequency of 25 Hz. According to an experienced LEOK department head, that frequency was too low. It would lead to inaccuracies due to lag and too much noise in the control of the cannon. He argued for 100 Hz. However, that would place a much greater burden on the fire control computer supplied by HSA. Therefore, HSA objected.
It was therefore decided to build a “digital cannon tester”. With this digital test box, the cannon could be controlled from both angles. The box, therefore, contained synchro-digital converters for measuring the position of the cannon and amplifiers for steering the cannon. The box also contained electronics to generate sinusoidal or other control signals and to add noise. Bandwidth and strength of the noise and the frequency of the digital generation of the control signal could be set. Relevant signals were recorded on an 8-channel paper recorder.
The test took place in 1972 onboard one of the old submarine hunters. Present were the Head of Quality Control of HSA, the LEOK department head and one of his employees. “It was a very special experience for me as a young employee. In the small space below deck, you stood next to the rotating ammunition drum with rattling grenades. It was quite noisy. Both experts laid their hands on the rotating and vibrating ammunition drum. For the experienced gentlemen that provided already a very good indication. Ultimately, a 100 Hz control frequency was chosen.