Dear Prasad,

if I'm not mistaking your question, there is a trivial answer to it.

The datasheets of the sensor/motor/drive will state a maximum current taken from the device and just as well the spec-sheet from the PLC will hold an information about the current that a correlated port can supply or take.

In case you got an issue with too little output current of a given port, industry holds amplifier ICs like the one linked to that can boost output to higher currents.

Cheers - Martin

http://www.infineon.com/isoface

You have to check the sensor and PLC specifications. Usually, the input of PLC and Data acquisition has high input impedance to receive less current and most of sensors are designed to deliver small current at their output except if there were designed for driving another system.

The inputs and outputs of an PLC's cards have specified current consumption. For example, as an input for PLC, the sensors realize an ON-OFF switch for activation of inputs. For the outputs cards, when PLC have relays, we know the value of current, as current limit of relay's contacts. When outputs card of PLC is based on transistors , we know the value of this current.

For a motor HP  and Voltage are specified. 1HP = 735.5 Watts.You can easily claculate the maximum current from HP and voltage data.   For a 3 HP,220V DC motor, maximum current = 3x735.5/220 =10.03A. Similarly you can calculate for other motors including AC motors. For all devices power rating and voltage are specified.from that data calculate the current rating. Accordingly select the cable that withstands this current.

You have to study specification sheet of sensor and signal conditioning circuit. However  sensor current throughout the operating range must lie between minimum and maximum current of PLC Input. e.g 4-20mA or 0-20mA.  Similarly study motor specification  and find out  capacity in KW or KVA of the motor. Select appropriate drive  at least  1.5 time higher the KW of the motor.  Input of the motor drive will match with the PLC output module in normal cases and will be no issue of problem.

You have see the datasheet of that sensor/motor because specification have all the parameters related to that product. You can also use current transformer to measure exact amount of current consumption. 

As the colleagues told previously, you could usually find necessary current using datasheets and some calculation. What I can add is a suggestion: always isolate input/output cards of PLC from sensors/Actuators. I mean, do not connect an input channel directly to a sensor or an output channel directly to an actuator. I/O channels of PLC are really sensitive and sudden over-current will burn them out. Burning out one channel in a card may cause malfunction in other channels too. Therefore, protect your PLC by isolating sensor/actuators using for example relays.

Dear

Prasad PANDURANG Patil

you have to choose appropriate driver for the motor and signal conditioning circuit (A/D D/A converter) for the sensor .That Automatically serves the purpose.PLC's can handle currents of 4 -20mA range. 

with regards

vasanth

There are two ways of knowing the current, the easiest is to search the data sheet sensor , drive or motor. The second would be measured with an ammeter current consumption . And based on that search specifications card inputs and outputs how much current it can provide. I personally think so will have good results.