lude risk for accidental errors in control algorithm. Special devices are well tested and generally free of this kind of problems. If available, it’s economically thoughtful to use special devices. РSafety applications that require highest degree of reliability should contain simplest devices and circuits possible. There is a rule that every new link in chain decreases overall reliability. РIn small applications it’s often cost saving to use relay-based circuits instead of PLC-s. Р3. FUTURE TRENDS РProgress in process automation systems is aiming at so plete automation when all the human has to do is to enter the parameters of the product wanted and everything else is carried out by machines (Rosin, 2000). Although the destination lies far ahead, trends indicate movement in that direction.
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