Question about Programmable Logic Controllers (PLC) and programming?

Is it possible for smaller Programmable Logic Controllers (PLC) to perform multiple tasks at the same time using the ladder language? (such as a single PLC simultaneously regulating speed and temperature)

Also, is it possible for PLCs to receive data from electronic switches in order to control software values instead of hardware and mechanics?

Absolutely. This is why they are so popular in industrial control applications. In fact most micro PLCs manufactured today are able to run multiple PID loops simultaneously. I've gotten into the trend of shying away from control designs with multiple individual process controllers and instead using one PLC with HMI to control things like temperature, valve position, or motor velocity.

As for the second question, it is common practice for PLCs to be controlled over a SCADA network or by a local Human Machine Interface (HMI) unit. You just have to be sure that the PLC that you choose and the device that you will be controlling it with are capable of the same communication protocol and network infrastructure. I personally find it simple to use Modbus TCP. Over an ethernet network, you assign everything a static ip address or let them DHCP, it's up to you. Then you can use the Modbus protocol to send and receive packets of data.

If you are still shopping around, check out some of the links I've posted. You can some PLCs that will do the things that your talking about for a relatively small amount of money.