A quantiser relates its inputs and outputs by a quantisation function as defined in the Quantised State Systems section. In the particular case of ModelicaDEVS/PowerDEVS, the Quantiser block is a non-hysteretic function similar to floor() that maps the input signal to the quantisation levels that are equidistantly distributed at values Qk= ± k*quantum with k=non-negative integers.
In other words, if we assume a quantum value of 0.1, then the y-axis can be thought to be "cut" into slices of height 0.1, since the quantisation levels are located at values of y=0.1*i for i=non-negative integers - at equidistant y-values starting from zero in both the positive and negative directions. The Quantiser block generates an output event whenever the input signal crosses a quantisation level. The output event takes the value of the current function value; hence it is a multiple of the quantum parameter value.
Note that this block is somewhat similar to the CrossDetect block, that however has a fixed output value and only a single level where crossings have to be detected.
The subsequent picture shows a sine signal quantised with a quantum of 0.4. The sine signal itself is plotted in blue, the quantised version in red.
.ModelicaDEVS.FunctionBlocks.Quantiser