DETAILED DESCRIPTION
INTRODUCTION
This document addresses the EMC Turntable Controller in particular a description of how the legacy controller has been modified to incorporate an optical sensor for turntable positioning feedback and computer control using a graphical user interface (GUI).
SETUP DIAGRAM
Figure 1 - Setup Diagram
TECHNICAL DESCRIPTION
The old turntable controller system KR-400RC is an analogue controller which made use of a feedback resistor in the AC motor assembly for turntable positioning which is displayed using a 360° analogue dial. The motor is controlled via two switches that turn the motor in either the clockwise (CW) or counter clockwise (CCW) direction. See figure 2 below of the controller.
Figure 2 - KR-400RC Controller[1]
The motivation behind upgrading this legacy system was apparent mainly because it required a great deal of manual work for conducting Radiated Emission (RE) pre-compliance testing. As frequencies under question become increasingly higher so to does the dwell time needed to measure those frequencies at various angles, meaning the test engineer has to pause the table every 15° for up to 50 seconds at a time to get an accurate measurement of the Equipment Under Test (EUT). This proved to be a long and inaccurate process due to the non-linearity of the analogue display, even after calibration.
KR-400RC Modifications Requirements
The requirements of the new design are to automate the turntables rotation with user specified inputs such as:
- Dwell time – How long the table will pause at a given angle of rotation.
- Step size – Each step will be 15° minimum, this setting determines how many steps are taken between each dwell time pause of the table.
- Manual angle – This allows the user to input any angle that is a multiple of 15° upon which the table will rotate without pausing. For use in measuring quasi peaks at the worst angle.
- CW and CCW controls – Incorporating the legacy control, can come in use in the quasi peak measurements to quickly change the angle CW or CCW.
- Calibration – This ensures the table and control software are calibrated to the same angle.
- Scan duration – The total time for the turntable automation to complete a scan.
- Use of the legacy control will not be decommissioned; the proposed automatic system is to work in parallel and isolation with the legacy system. In case of failure of the new system, test engineers can revert back to the old system control.
- Sensor failure/error - There needs to be a safety element implemented that detects a failure/error/false triggering of the sensor that will prevent the table from rotating.
Modification integration with legacy system schematic
Below in figure 3 is the schematic of the legacy KR-400RC controller with the addition of the modification circuitry, simply the modification makes use of solid state relays in parallel with the legacy control switches to control power to the AC motor via a Arduino Pro Mini uC.
Figure 3 - Mod integration with the legacy system
Control Software
The software used to control the uC is a C# windows forms application using USB COM Port communication. The software auto connects to the controller upon opening and will prompt a message upon failure with an option to manually attempt connection. Calibrating the table when starting a day of testing is encouraged, throughout the testing day the software will store in memory the position of the table to prevent having to calibrate the software multiple times when terminating the application.
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