HNC PLC assignment help

[Doowy]

Hi, I know there is a similar question already running but I have the same problem with different parameters? We are probably on the same course. I am on 1st year HNC and need a PLC for the following parameters: I have spent all day with no joy


I need

PLC power supply 240v, 50Hz and 110v, 50Hz
No. of relay outputs, 4 max rating 1mA each
No. of transistor, triac or thyristor outputs - 1
No. of contact closure inputs - 6
No. of 3 line proximity devices - 1 (unknown rating)
No. of analogue inputs - 1 0-10v dc
RS 232 or similar interface
Required memory 2k
Scan time better than 50ms


IP67 standard protection and external ambient temp -40C ( think we need anticondensation heaters in the enclosure for this?)

The PLC is housed close to a high frequency source of magnetic interference.


One output drives a contactor to switch a heating element of 240v, 20 A rating. Suggest the type of contactor and will the PLC be able to control the contactor coil directly?

Any help/direction is greatly appreciated

 

[Steve Bailey]

I have spent all day with no joy

What brands/models have you looked at and why did you reject them?

 

[Doowy]

I started looking at Mitsubishi Melsec A1S as it met the voltage spec but am struggling with the CPU spec.

I am really new at this and am finding it hard to match the voltage and then find anything to go with it. My problem is probably that I don't understand most of the question and was just after a bit of advice.

I was pointed in the direction of Allen Bradley SLC 500 but I dont think it does match the voltage spec, neither do the PLC5 or control Logix.

I just need a point in any direction

 

[Steve Bailey]

The voltage level required to power the PLC is independent of the voltage level required for the inputs and outputs.

Relay outputs are contact closures. They are capable of switching a wide range of voltages. What do you think you need to watch for if you need the PLC's outputs to control devices operating at different voltage levels. Hint: look at the PLC's output wiring diagram.
Transistor outputs must operate at a voltage level corresponding to the type of transistor. Some may operate at 5 VDC, others in the 10 -30 VDC range. Triacs are AC solid state switches.

Most PLC inputs can connect to solid state devices (like proximity or photoelectric sensors) or contact closure devices (like limit switches).

Typical analog sensor operating ranges are 0 - 10 VDC or 4 - 20 mA. If you apply ohm's law, you'll find that with a 250 ohm resistor, a 4 - 20 mA device can furnish a 1 - 5 VDC signal range. You can apply a 1 - 5 volt signal to a 0 - 10 VDC analog input channel, but what do you think you're giving up when you do?

 

[iant]

the PLC power either 110V or 240 V 50Hz seems to tie you down.
A majority of countries and companies are pushing for segregated power systems - ELV and LV seperated (24Vdc / 240V)
consider a switchmode power supply. - this free's up the choice of range of PLC. your only restriction should be the Scan time (50ms)
- Outputs
If you need to switch Loads greater than 3 Amps RESISTIVE then look at interposing relays/contactors.
Speed of switching and type of switching as mentioned by steve