PLC digital output module selection

Output modules are PLC internal low voltage signal can be converted to an external output device required to drive signals. Main load voltage should be considered when choosing the type and size, system requirements, to delay load state changes are frequent, and so on.
 
1. Choice of output
Digital output modules have three output: relay output, transistor output, transistor output. Relay output of cheap, can be used for driving load, and can be used for DC loads, but also a wide voltage range, conducting small pressure drop and ability to withstand transient overvoltages and currents strong. But it belongs to the contact element, with the movements slow, short life, poor reliability and, therefore, can only apply to frequently pass situations. When used for driving inductive loads, and the contact frequency is less than 1Hz.
For frequent switching of the load, use bi-directional thyristor or transistor output, contactless symbol they belong to. TRIAC output can only be used for AC load, and can only be used for the DC transistor output.
 
2. The choice of output connections according to the output of the PLC connection of different, separated generally grouped output and output two,
As shown in Figure 5-16.
Grouping output is output as a group, sharing a common Terminal, is a separation between the groups may use different power supplies. Separated output each outputs have a common, mutual isolation between outputs, each output can be used with different power supplies. Mainly according to the system load of the power supply may be. General integral PLC group output, separate output.
 
3. The choice of output current
The output current of the output module (drive) must be greater than the rated current of the load. Users should be based on the actual load current of the selected module‘s output current. If the actual load current is large, output modules cannot be directly driven, can increase the enlargement process.
 
4. Number of output points while connected
Select the output module, the number of simultaneously connected to the output points should also be considered. While connected to the cumulative output of allowable current value must be less than the public side of the current value. 8 points as a 220V/2A output module, each output current of 2A, output publicallows current 16A (8X2) is usually much smaller than this value. In General, and access points do not exceed 60% of the same common Terminal output points.
 
5. Maximum load current of the output and the type of load, ambient temperature and other factors