New to PLC, Help needed for a project

[Arvind rangarajan]

Hi,

I am working on a project where i need to automate a process that involves around 5 to 6 steps roughly. I have Radio Frequency glow discharge equipment connected to a vacuum pump. The sequence of operation goes like this,

1)close hatch after placing the equipment inside.
2)switch on vacuum pump ( acheive a pressure between 0.15-0.2 torr)
3)switch off vacuum pump when pressure drops below 0.20 torr
4)inject 50% concentration hydrogen peroxide through the valve in the hatch.
5) wait for 15minutes so that the hydrogen peroxide diffuses and spreads to all parts of the material kept.
6) start vacuum pump again and simultaneously initiate glow discharge for 10minutes
7)shut off glowdischarge and vacuum pump
8) re-pressurize the chamber by letting air inside

( all this sequence should start with a Push Button)

I will be using the following sensors ( temperature sensor, negative pressure sensor, door proximity sensor, hydrogen peroxide gas sensor, current sensor).

Please guide me on what are the things i should know about before buying a PLC for this project. Also, let me know if there are any low cost PLC kit that i could buy online. I would like to integrate the PLC with my laptop. I am just learning the basics of PLC. For your reference, i have also attached the pictures of the device that i am trying to automate.

Thanks ,

Arvind

 

[dploof23]

Hi,

I am working on a project where i need to automate a process that involves around 5 to 6 steps roughly. I have Radio Frequency glow discharge equipment connected to a vacuum pump. The sequence of operation goes like this,

1)close hatch after placing the equipment inside.
2)switch on vacuum pump ( acheive a pressure between 0.15-0.2 torr)
3)switch off vacuum pump when pressure drops below 0.20 torr
4)inject 50% concentration hydrogen peroxide through the valve in the hatch.
5) wait for 15minutes so that the hydrogen peroxide diffuses and spreads to all parts of the material kept.
6) start vacuum pump again and simultaneously initiate glow discharge for 10minutes
7)shut off glowdischarge and vacuum pump
8) re-pressurize the chamber by letting air inside

( all this sequence should start with a Push Button)

I will be using the following sensors ( temperature sensor, negative pressure sensor, door proximity sensor, hydrogen peroxide gas sensor, current sensor).

Please guide me on what are the things i should know about before buying a PLC for this project. Also, let me know if there are any low cost PLC kit that i could buy online. I would like to integrate the PLC with my laptop. I am just learning the basics of PLC. For your reference, i have also attached the pictures of the device that i am trying to automate.

Thanks ,

Arvind

Click PLC's from Automation Direct are inexpensive and the programming software is free. I believe they recently added temperature input so it should be able to handle all of your needs nicely.
Hope this helps,
Dave

 

[mattjsayers]

I will be using the following sensors ( temperature sensor, negative pressure sensor, door proximity sensor, hydrogen peroxide gas sensor, current sensor).

Questions:
What type of signal do these sensors put out? (List each) ie(analog 4 to 20 ma, or 0 to 10 dcv, or limit switches etc.)

 

[Lancie1]

Yes, getting sensors and a PLC that will accept the signals for all of them will be a key to making it work. For the 8-step program, almost any PLC will be able to do the logic, but not all will be able to read in the various kinds of analog signals from your sensors. So you need to carefully check the specifications for each sensor and see if you can find a PLC Analog Input Module that will read that signal.

The Door Prox sensor will be a digital input (on/off type and cheaper). The others will be analog (continuously varying from 0 to some maximum amount and more expensive).

There are combination measuring devices with relay outputs that have external settings where you set a range that you want a relay output to go on and go off. Then those digital outputs can be fed into your PLC as on/off signals instead of analog. That method is not very satisfactory or accurate.

If you can find temperature, pressure, gas detector, and current sensors that have current outputs of the range of 4 to 20 miliamperes, then you can buy almost any brand and model of a mid-size mid-price PLC that will have built-in or add-on Analog Input Modules that accept 4-20 mA signals. For the temperature, current, and vacuum signals, I know there are many models of signal transmitters that will produce the 4-20 mA output. For the gas detector, your choices will be more limited (and expensive).

 

[Arvind rangarajan]

I have not bought the sensors yet,i will buy it soon. I will be having 3 analog sensors ( temperature (4-20 mA), pressure (4-20 mA), hydrogen peroxide gas,) and 1 digital proximity sensor ( 4 vdc). I am planning to get all the sensors from OMEGA. So do i need to buy a PLC that has atleast 3 analog input slots ? and i will have 2 outputs to control the vacuum pump and RF oscillator through relays. Please guide me on what low cost PLC will serve this purpose. I also want to know if i can control the sequence using PUSH BUTTON from the computer.

 

[Arvind rangarajan]

I also need to know what kind of relays to buy that will switch on/off the vacuum pump and RF oscillator. What will be the output from PLC that will trigger the relays? Will the PLC output be in mA or Volts ?

 

[Arvind rangarajan]

Sorry, i forgot to include the LCD display. I will also be needing a display unit to show what process is going on at a given instant. Will a PLC with display unit help?

 

[Lancie1]

I think the Automation Direct CLICK PLC would be capable and economical.

You could chose the following CLICK model:
CPU: Model C0-01DD1-D with 8 digital Inputs and 6 digital Outputs
Add-on I/O module: C0-04AD-1 with 4 analog inputs
Power Supplly: C0-01AC, 120 VAC in, 24 VDC out at 1.3 Amps max.

If you want pricing for the above, go to AutomationDirect.com

http://www.automationdirect.com/adc...lers/CLICK_Series_PLCs_(Stackable_Micro_Brick)

Based on your description and current equipment you would not need this, but if you want to control anaolg devices, such as a variable speed vacuum pump, or the concentration of hydrogen peroxide using valves, then you would also need some analog outputs, such as the CO-04DA-1 4-channel 4-20 mA Analog Output Module.

A graphic operator display is usually a separate item that communicates with the PLC with a cable. There are PLCs with very limited built-in displays and Automation Direct has those too. I think you would be better off with a separate unit that you could mount at a convenient position (not necessarily the same place as the PLC).

 

[Arvind rangarajan]

Thank you very much guys!! I will get back if i have more questions, once i start wiring the devices.

 

[Lancie1]

For starting and running the vacuum pump, you will need an external relay with a 24 VDC coil and contacts rated for motor starting at the starting current rating of your vacuum pump. For the other digital outputs (hydrogen peroxide valve solenoid, glow discharge, hatch closing) the external output relays can be cheaper models with a lower non-motor contact current rating.

 

[strantor]

How are temperature and analog prox values used in the logic? You didn't mention those in your 8 steps. Do you really NEED an ANALOG prox with pesky 0-4v requirement? Would a digital one suffice? Since you want LCD readout of (pressure?) And (temperature) you can use scalable panel meters with relay outputs from the likes of red lion or omron. This saves you needing an analog card for the PLC. Actually, depending on your answers to my above questions, it could even save you needing a PLC. If you only need one timed event, you could use a din mount timer relay for that, and handle the rest of the logic with a couple of relays.

 

[Arvind rangarajan]

The temperature inside the chamber during RF gas plasma treatment is nearly the room temperature +/- 1 degree celsius. However, for quality control purpose i need to really check if the temperature inside the chamber is really the room temperature or not. I do not want the output of the temperature sensor to trigger any event.

The digital proximity switch will be needed to start the sequence of event described above once the hatch is closed. I do not want the vacuum pump to be running without the hatch being closed.

Please let me know if there are any other things i should consider.

Thank you

 

[shooter]

forget the door, it makes it complicated, just switch on the PLC and it should start your program.
any analog sensorinputs are expensive so if you do not really need them, use switches. the pressure switch is easy get one of these washing machine levelswitches work fantastic.
for the vacuumpump use a simple relais
and you will need a solenoidvalve in the hydrogen line.

 

[Lancie1]

for the vacuumpump use a simple relais

Yes, simple, but rated for 0.75 horsepower motor starting or more. From the picture, the vacuum pump will require a large starting current.

 

[strantor]

Will you be metering the amount of peroxide solution (if so, how?) or will it be a timed discharge cycle or what?