Abstract : This paper analyzes the causes of defects in the start-up circuit of the Bardak jig and makes improvements to meet production needs. Keywords : control contactor relay timing coordination. The three German Bardak jigs introduced to the Dongqu Coal Preparation Plant have proven through several years of production operation that the equipment has an advanced structural design, a high degree of automation, and microcomputer control in all aspects. However, we found that the start-up circuit of these three jigs had a problem with improper timing coordination between the control electrical components, directly affecting the smooth operation of production. We made improvements to the circuit and made several attempts, finally achieving a 100% start-up success rate. 1 Problem Statement When the operation mode selection switches of the jig and the coal feeder are all set to the "automatic" position, the centralized control device (located in the centralized control room) issues a start-up command for the jig, and the jig can start running. However, at this time, it has not yet entered the coal preparation operation state; it is only in its preparation stage. After about 1 minute (set by the centralized control device), the centralized control device issues a start-up command for the coal feeder, causing the jig to enter the coal preparation operation state. However, due to improper timing coordination between the relays and control contactors in the starting circuit, the action sequence was reversed, resulting in a false alarm signal and failure to start the machine. The main circuit of the coal feeder and part of the control circuit are shown in Figure 1, and the control circuit of the heavy-load relay is shown in Figure 2. [b][align=center]For details, please click: Improvement of the Starting Circuit for the Bardak Jig Coal Preparation Machine[/align][/b]