plc analog io modules and how to convert digital

The concept is relative to the analog digital (switch) is, the digital signal is a signal that the signal is only two states 0 and 1, such as our trip switch button.
Is a discrete analog signals, plc analog io modules Analog data within a certain range, Ken can be any value, such as pressure, temperature, flow rate can be either a voltage can be 0.1 0.12 etc. When we deal plc sequence of events module  with such signals, with analog modules! Equipment such as temperature and humidity into analog signals need to use analog modules, analog module includes voltage, current, RTD, thermocouple module may cause the input signal voltage value of less, depending on your 0 - 10v with a  Programmable Input Module load capacity of how kind, because this time the input impedance of 250 ohms, then the maximum current can reach 40MA, the voltage signals are generally not such a big load capacity, in fact, the current input is converted to 4-20ma to 1 - 5v voltage before making A / D conversion. If the 0-10v enough to do with a load capacity may exceed the input limit, unless your plc modules are set in accordance with 0-10. Here is not required for transformation, when entering plc analog input module via analog, through conversion (programming calculation), the corresponding temperature value, then according to pulse input module plc  your set of 100 degrees Celsius to compare the size (programming), when greater than 100 degrees, plc control output IO module enables equipment downtime too, of course, out of the signal may be digital. Because just a simple switch, very simple.