Exercise DET-02.03 – Secure press operation

Prof. Dr. Thorsten Jungmann (last updated 2026-10-12)

Relates to DET-02 Logic operations

Task

A press in a car factory may move down only if its guard is closed ($A$) and the operator presses its two buttons, one with each hand ($B$ and $C$). The output is $Y$, ‘press may move down’. Subtasks a) and b) are based on exercises in the textbook by LaMeres [5, pp. 84–85].

a) Set up the truth table of $Y$.

b) Sketch the timing diagram of $Y$ when the inputs $A$, $B$ and $C$ run through all eight combinations one after another, in the order of the truth table and each for the same time. Assume an ideal gate without delay.

c) Draw the contact logic of $Y$ between the rails L+ and L−.

Solution

a) $Y=A\cdot B\cdot C$; $Y$ is 1 only in row 7, where all three inputs are 1
b) $Y$ is 0 in the first seven sections and 1 only in the last of the eight sections
c) three normally open contacts $A$, $B$ and $C$ in series with the lamp $Y$

▶️ Full worked solution