When you use proportional control, the following sequence of events takes place.

• Measure the output of the system.  Call that value Measured Output.
• Compute the error as the difference:
• Error = Desired Output - Measured Output
• Compute the control effort by multiplying the error times the proportional gain.
• Apply the control effort to the controller.

In the diagram above, we assume the following.

• The output is measured on some remote computer, and is available over a network using a TCP/IP connection.  That TCP/IP connection is established in the TCP/IP Open Connection block outside of the while loop.
• The TCP/IP Oopen Connection block requires the user to input an IP address for the remote computer and the number of the port used to transmit the data by the remoted computer.
• The measurement data is a string.  That string will have a length longer than 10, so that the length - expressed as an integer - has two digits, and that information is input to the first TCP/IP Listen block inside the while loop.
• The string length is decoded in a Scan-from-String block, and the integer output from that block is used as an inpout in the next TCP/IP Listen block.
• The second TCP/IP Listen block gets the string that actually contains the measurement data, and uses a Scan-from-String function which has an exponential/fractional output to generated numerical data.
• The Measured Output is subtracted from the Desired Output (in a subtractor block) to form the error.
• The error is multiplied by the proportional gain in a multiplier block.  That gives us the calculated Control Effort.
• Since this is a numerical computation, the output of the multiplier - the Control Effort - is a number.  To transmit the Control Effort to the remote computer requires that the Control Effort be changed into a string format.
• We use a 2f.3 format which gives a string of the form xx.yyy.
• The length of the string is calculated - as a number - and converted to an equivalent string and transmitted to the remote computer.  The first piece of information sent to the remote computer is the string length.
• After the string length of the Control Effort string is sent, the actual Control Effort string is then transmitted to the remote computer.
• The while loop continues forever, or until the connection is terminated.

Note the following in the front panel.

• You can input the port to use.  Choose any unsed port.  The one shown, 2055, is a good choice since it is unlikely to be used by anything else in the system.
• The address must also be entered.  Although it shows localhost when the vi loads, you should type the IP address of the remote computer there.  The form is www.xxx.yyy.zzz, the standard format for IP addresses.
• Information you can enter here is:
• The desired output,
• The proportional gain.
• Information displayed is:
• The Measured Output - numerically and on a "thermometer" display.
• The Error - numerically and on a "thermometer" display.
• The number of iterations the loop has run.