FAQ
Question:
How does PLC systems cabling work?
Answer:
Wiring with the system cabling considerably reduces the assembly time and guarantees protection against polarity reversal.
The first part of the systems is the card adapter. These front adapters with an integrated male ribbon cable connector (IEC 603-1 / DIN 41 651) are plugged onto the PLC I/O card. In order to plug in the adapter the original hard-wire swing arm must be removed from the card to expose the connection points for the plug adapter.
The second part of the system is the field interface board. These interface boards are simply snapped onto the mounting rail instead of modular terminal blocks or coupling modules. On the control side they also have a multi-position male connector (ribbon cable type).
The interface boards are connected to the front adapters using multi-position and preassembled system cables.
Question:
Why does Phoenix Contact use two cables for 16 channel cards?
Answer:
There is a very good reason for this. Most PLC Manufacturers state a worst case scenario of having ½ of the total output channels activated (8 of 16). On a typical 16-channel output card, each channel is rated at 0.5A. If ½ the channels are on, there would be a total of 4A flowing through the I/O. Since the supply voltage and current for the card originate on the breakout module, all of the summed current must flow through the cable between the I/O card and the module.
For the 16 channels of I/O, Phoenix Contact uses two 14 pin cables. Each cable contains 8 pins that are used for 8 channels of I/O and 6 pins that are used for the voltage/current supply to the card. For the positive supply, 3 pins are used and for the negative return another 3 pins are used.
Per UL, a 26AWG conductor is only rated at 2A. One conductor is not enough to supply the 8 channels with the required summed current. Phoenix Contact utilizes 3 conductors per potential (+,-) to supply the voltage and current to the card. This means per 8 channels of I/O, there is available capacity for 6A.
Phoenix Contact has built the PLC-Cabling solutions to meet and even beat the maximum worst case scenarios of most cards. This allows the solution to be used on a wide array of I/O cards.
There is also a secondary reason for having two cables for 16 channels. Not every user needs 16 of one type of input or output. Some users mix functionality on the I/O cards. Splitting the boards out to two groups of eight follows the voltage supply of most I/O cards where every group of 8 has their own voltage supply (1 byte). This will allow the user to have fusing on one set and relays on the other. This offers a greater range of flexibility in the control cabinet.
Question:
Can I connect sensors and actuators to the PLC-cabling system?
Answer:
Yes. Both sensors and actuators from the field level are connected to the controller boards by means of screw or spring cage connection, or knife disconnect terminal blocks. The interface boards are marked on the field side according to the application, so that the signals can be clearly assigned.
Question:
Can I connect thermocouples and thermocouple cards to the PLC-cabling system?
Answer:
No. The reason for this is the incompatibility between the connections of the cable header and the terminal blocks where the thermocouple would be connected. Because thermocouple cards are designed specifically for specific types of thermocouple wiring, there is a material incompatibility with a cabling system.
The type of cabling that Phoenix Contact uses for standard PLC-cabling solutions is not conducive of a thermocouple wire. At the connection point where the thermocouple wire would be connected to the module, the terminal block would have to be a specific type of material as well as the cabling material itself.
To use thermocouples with a PLC-Cabling solution a different type interface is required. Typically an analog input card would be used in conjunction with a specific Temperature in / Analog out conversion module. This would allow the connection of a thermocouple outside of the control cabinet and using standard copper wire to connect to the controller.
By using an analog card versus a dedicated thermocouple card not only saves money in card costs but also in rack density. Most thermocouple cards are only two or four point modules. By using an eight or sixteen channel analog input module, the density of connecting multiple thermocouples on a single card can be multiplied by as much as eight times.