View Full Version : PLCs for control of valves, motors...
May 16th, 2002, 12:50 PM
I am new to PLCs (i am an undergrad student doing an internship at a company) and my boss has purchased Trilogy Research International's T100MD888+ PLC.
Now that i understand how PLCs work and the ladder logic/TBasic programming involved, i'd like to understand how this may be applied to controlling valve openings, stepper motors... I know this probably seems like a simple question to most of you, but i would appreciate some guidance or examples.
Thank you in advance.
May 16th, 2002, 01:21 PM
I'm not sure I understand your question.
Are you asking how, physically, the PLC gets the valve to move, or how you go about writing a program to move the valve?
(Lets keep stepper motors out of this for the time being and stick to regular motors. Some steppers will function like regular motors and go through their program on the high of a input to the motor/from the PLC. Others talk via RS-232 and want more info from the PLC.)
May 16th, 2002, 01:50 PM
Your question is really to general to answer properly. Conceptually, you have the world divided into the PLC and field devices. The PLC has inputs - it is reading the status of the field devices. Inside the PLC you have rules - your ladder logic program - that regulate what the machine is supposed to do. The PLC has outputs that, based on the result of the inputs plus the rules, activate the field devices. Thats all there is to it!
Simple example - a PLC replacing the thermostat in your house. The field devices are the high and low temperature switches and the heat and cool inputs (wired to the inputs to the PLC), the burner, the fan, and the air conditioning compressor (wired to the outputs from the PLC).
The rules are:
Heating selected, temperature switch low on, start burner, delay, start fan. When temp switch high comes on stop burner, delay, stop fan.
Cooling selected, temperature switch high on, start compressor, delay, start fan. When temp switch low comes on stop compressor, delay, stop fan.
Have you read Phil's tutorial and bought his book? What specifically do you need to know?
May 16th, 2002, 02:41 PM
Depending on the voltage you apply to your valve, than it opens more or less.
May 16th, 2002, 03:09 PM
To program your PLC you must connect the board through its RS232 input to a computer. To load your PLCs CPU, press enter in ladder logic software. Make sure that your ladder logic is correct, because if not you cannot erase or make changes to your PLC. You will have to buy a new one.
May 16th, 2002, 05:04 PM
I dont think statements like that are needed PLC...looks like its back.
Haps as stated above your question is too general. With plc's you can use discrete (digital) I/O to get signals in from devices likes switches or turn on or off devices like contactors/motor starters, solenoid valves etc...ie any device that is on or off. Analog I/O offers options for varying voltage/current...input devices like thermocuple, load cells etc..output devices like proportional valves, actuators etc. There is also communciation options like RS232 and more that can talk to devices ...inverter for one.
Since the T100MD888 has analog I/O, PWM, and stepper motor controller built in I would suggest reading their manuals a little more in detail..They also have a forum that may have better detailed answers:
December 19th, 2003, 03:02 AM
i am working in aautomation company .i am company my duty is to programming in plc .i have knowledge in plc programming but i does not know about lcd interfacing program. so plese send me program for keyence plc ladder program .