Choice of direct current power supply for Discrete I/O sensors and pre- actuators

Choice of direct current power supply for Discrete I/O sensors and pre-actuators

At a Glance The following is a presentation of precautions for choosing sensors and pre-actuators associated with Discrete I/O modules.

External direct current power supplies When using an external 24 VDC direct current power supply, it is advised to use either:  regulated power supplies;  non-regulated power supplies but with the following filtering:  1000 microF/A with full-wave single phase rectification and 500 microF/A with tri-phase rectification;  5% maximum peak to peak ripple;  maximum voltage variation: -20% to +25% of the nominal voltage (including ripple). NOTE: Rectified power supplies with no filtering are prohibited.

Ni-Cad battery power supplies This type of power supply can be used to power sensors and pre-actuators and all associated I/Os that have a normal operating voltage of 30 VDC maximum. While being charged, this type of battery can reach, for a duration of one hour, a voltage of 34 VDC. For this reason, all I/O modules with an operating voltage of 24 VDC can withstand this voltage (34 VDC) for up to one hour every 24 hours. This type of operation entails the following restrictions:  at 34 VDC, the maximum current withstood by the outputs must under no circumstances exceed the maximum current defined for a voltage of 30 VDC;  temperature downgrading imposing the following restrictions:  80% of I/Os at 1 at up to 30°C;  50% of I/Os at 1 to 60°C.