Introduction to Industrial Automation

2.3.2   Cam  Timers

Cam timers, or motorized drum switches, are electromechanical sequencers used in industrial 

applications with repetitive processes of a finite number of steps. They are considered an old-

fashioned type of timer, due to the current PLCs where such timers can be easily programmed, 

but for small automation applications they are an appropriate solution, even today. Furthermore, 

their operation knowledge helps students to better understand the industrial processes, including 

a sequence of successive and interrelated ON-OFF operations of different machines. Figure 2.58 

shows a general view of a multiple cam timer consisting of a motor, a gearbox, a setting disk, 

dual cams, and limit micro-switches. Details of its construction are shown in Figure 2.59 for a 

five-cam timer. The synchronous motor rotates the camshaft continuously through a gearbox 

with a constant cycle time period, usually of 1 min. This means that a full rotation (360°) of 

the camshaft takes 1 min. Several other cycle times, from 12 s to 24 hrs, are available from 

manufacturers.

The camshaft carries a number of fix-mounted dual cams with the ability to adjust their initial 

position. The number of dual cams may vary from 1 to 12 or even more, according to the applica-

tion needs. Each dual cam has two separated sides, each of which can slide concentrically with 

respect to the other. The periphery region of each cam-side is properly formatted in order to form 

a groove angle in each cam by sliding, as shown in Figure 2.59. Obviously, the value of the groove 

angle corresponds to a defined constant time interval per cycle of operation. In front of dual cams 

there are an equal number of leaf-spring-mounted limit micro-switches, each with DPST elec-

tric contacts that are wired to devices on a machine for ON-OFF control. Therefore, adjustable 

hand cams can turn the micro-switches on and off, and the switches can be adjusted at specific 

times within an operation cycle, hence they can “program” any sequence of operations that will 

be continuously repeated. Multiple cam timers are often referred to as time-step programmers,