process variable

Each machine has a set of process variables and profiles. A process variable is a physically, measurable quantity or characteristic that is collected by a DCM. Most process variables are collected once during each machine cycle. Examples of cyclic process variables are temperatures, pressures, time durations, and PLC readings. Some process variables are not directly related to machine cycles. Examples of non-cyclic process variables are manually operated scales and gauges. Process variable names can be up to 20 characters in length.

There are several categories of process variables. A process variable's type is determined by the source of its input signal:

·	Cycle Time - Obtained through the primary contact input. Cycle time is the time between consecutive closures of this input. This is always the first process variable.

·	Analog Channel - Obtained by reading one of the analog channels within a DCM. The applied signal may originate from a pressure transducer, linear potentiometer or another linear device.

·	Duration - Obtained through an additional contact input. A duration variable measures the length of time that a contact input was closed. One example is hold time.

·	Serial Communication - Obtained through a serial communications link with the machine's controller. This type of process variable requires a specific software driver. An example is an Engel PLC.

·	Pseudo - Obtained by reviewing a profile. This may be the maximum, the time that the maximum occurred, the minimum, the time that the minimum occurred, the range (max - min), or the average of the selected profile. Examples include peak pressure, peak time, stroke, and cushion.

·	Thermocouple - Obtained by reading an analog channel where a J or K thermocouple is connected. This is used in temperature measurements.

A profile is a rapidly changing process variable, such as pressure or position. For a profile, a machine's DCM collects a set of up to 500 points per machine cycle. Profiles are mostly collected from analog transducers. Some PLC's are capable of collecting and transmitting a profile.