FAQ
Q: Are there any operating problems with the 120 V ac and 230 V ac versions?
A. Due to the low current consumption of the PLC-RELAY, the PLC-RELAY could remain energized even when switched OFF. The problem is associated with the use of Digital Output PLC cards that have a TRIAC output, and occurs because the OFF State of the TRIAC is between 2mA to 8mA.
To work around this problem the suggested practice is to use digital output cards with a 24 V dc voltage level. This not only reduces the current consumption, but also increases the density of the PLC. This practice also reduces PLC Rack size, and is more economical.
If the products are already installed and wired, the addition of a bleed-off circuit is the only remaining solution. In order to calculate the correct componentry, it is suggested that the current flowing in the OFF State be measured. While the easiest component would be a resistor connected in parallel to the input terminations, the solution requires the use of a high wattage resistor that adds an additional heat source in the control system.
Phoenix Contact recommends the use of an series R/C (resistor / capacitor) network connected across the input terminations that can be determined from the following ranges;
Resistor range from: 100 to 220 ,
Capacitor value from: 220 nF to 470 nF.
The solution is considered optimum since the addition of capacitor to the resistor reduces the heating effect in the resistor, and the circuit is able to run cooler.
Using the PLC-RELAY with PLC Output cards - Due to the benefits of the high density package, the use of the 24 V dc PLC-RELAY should be considered as the relay of choice when connecting the PLC-RELAY with a PLC. This solution provides maximum cost reduction to the PLC and relay combination.
