Personal Project - need suggestion - PID + thermocouple cheap !?

[JNTurcotte]

Hi Everyone,

While searching on the internet, I found out about this forum.
Looks like a great gang that is really helpful to others. Hopefully, I can help some others here, even if I am far from a plc expert.

But I am requesting your help and suggestion here since I wasn't able to find the answer after multiple hours on the internet.

I am building a herp room (multiple reptile enclosure in a room at my house).
For now, I am using a lot of individual proportional temperature controler.

My project is to use a PLC and possibly an HMI to control them.
Unfortunately, price is quite important here as it's a personal project and I would it to cost less than buying the individual controlers.

So I need to control from 4 to 8 (possibility of adding more) heat elements (heat tapes). Theses heat elements are 120V and will generate up to 120 watts at full power.

I want to control theses individually with PID.

I found out about AutomationDirect 05 and 06 models, but I am worry that they can't have enough PID running at the same time and that the number of thermocouples input cards are low.
The 05 model only have 1 possible io cards and don't have any ethernet cards.

I am looking for a PLC instead of the singles controls that I have, cause I want the temperature to adjust with the days/night and cycle with the seasons. And I would prefer a PID to a proportional elements.
I am also hopping to use the Inputs/Outputs to control other device in the room eventually.

I would like to add an HMI to make modification on the temperatures and testing. But can't seem to find a basic hmi for a reasonable price. Is it possible to have a plc with ethernet communication, and communicate with it throw a web page ?


If anyone could point me to a cheap PLC with PID and thermocouple solution, I would appreciate.
And some cheap HMI solution, it would be even better.

Thank You !

 

[leitmotif]

What is total value of the snakes?

IF you have one "brain" ie PLC controlling all what is the consequence of it failing?

What about power loss? DO you have standby power of any kind?

Montreal in winter sounds cold to me. Have you considered moving to a more temperate ie snake friendly environment?

Off top of my head I would
1. Ensure I have adequat power and backup power to supply demand of load ie heaters for say 4 hours or worst power outage in the utility history.

2. I would have a list of what I want to control and break that into 3 parts - right now - later on - dream list.

3. Ventilation ?? CO2 control?

When done with all that then start looking at PLC. Do not forget to find a a local rep and talk with him. In your case when you need help you need it NOW and you need repair parts in minutes to hours. Internet is great but count on
at least 3 days for help and the ANSWER
another 3 days for the repair parts.

Dan Bentler

 

[keithkyll]

Automation Direct 205 with 260 CPU. For HMI, the cheapest TFT color in the US is the mt6050i from Weintek. Software is free.
From China, the cheapest is the Samkoon SA-3.5A. It's a bit slow with the 200Mhz processor, but it works. Best price including shipping.
If you buy Weintek from China, Weintek USA will make it clear that they won't give you support. You must ship back to China for warranty, etc. Makes sense to stay in US with Weintek.

 

[JNTurcotte]

leitmotif : Thank you for your reply.

My collection price is something that I keep secrets and it's value fluctuate every year. But it is worth some thousand of dollars at least.

Yes Montreal can be cold during winter and pretty hot in summer.
I have everything already in place, AC, powersupply etc... (no generator unfortunately for now).

I am an industrial engineer, and have some contacts in case of emergency that I can't solve myself.

I am worry of a fail in of the PLC, program or some other device, but it's not different than what I am using right now.
The controlers that I am using now are HerpStat pro models, they can control up to 4 device and cost 500$. They are proportional and have night drop possibility but no calendar and it's impossible to keep track of variation of temperature.

I would like to have a small cheap plc that could control 4 zone to 8 zone and would cost less than 125$ per zone.
I could have multiple of theses cheap plc hooked to a HMI to control them (is it possible ?).

The equipment that I am using at my work are just too expensive for that kind of project unfortunately.
I might have to wait for price drop otherwise.

 

[OkiePC]

I am building a herp room (multiple reptile enclosure in a room at my house). For now, I am using a lot of individual proportional temperature controller.

I would investigate a PC based I/O and HMI for the most bang for buck.

There are some incredibly cheap USB dataloggers with multiple channels available and you then have only the challenge of getting that data into the HMI (usually via OPC server or direct driver).

My project is to use a PLC and possibly an HMI to control them. Unfortunately, price is quite important here as it's a personal project and I would it to cost less than buying the individual controlers.

Free HMI with Eyecatching Graphics

So I need to control from 4 to 8 (possibility of adding more) heat elements (heat tapes). Theses heat elements are 120V and will generate up to 120 watts at full power.

I want to control theses individually with PID.

So you are into the $1000 dollar range for nearly any brand of TC module in PLC land. I would look at some of the field I/O companies that support Ethernet/IP or OPC connections to Archie's free software.

I found out about AutomationDirect 05 and 06 models, but I am worry that they can't have enough PID running at the same time and that the number of thermocouples input cards are low.
The 05 model only have 1 possible io cards and don't have any ethernet cards.

I am looking for a PLC instead of the singles controls that I have, cause I want the temperature to adjust with the days/night and cycle with the seasons. And I would prefer a PID to a proportional elements.
I am also hopping to use the Inputs/Outputs to control other device in the room eventually.

This makes me lean toward an external datalogger for analog and PLC or plc style remote I/O for the stuff between 1 and 5 amps.

I would like to add an HMI to make modification on the temperatures and testing. But can't seem to find a basic hmi for a reasonable price. Is it possible to have a plc with ethernet communication, and communicate with it throw a web page ?


If anyone could point me to a cheap PLC with PID and thermocouple solution, I would appreciate.
And some cheap HMI solution, it would be even better.

Thank You !

A red lion G3 HMI has excellent hardware reliability boots and communicates in seconds. I love them and wouldn't hesitate to use a $1000 G30x HMI with PID logic in the HMI and/or connection to some of their modular controllers (which I have no experience with yet). This will be pricier, but very low effort and low maintenance and reliable, supporting remote viewing and/or control and the ability to log data and send it to a remote FTP site or database.

PLCs are great and all, but I would make this a PC based project to save money.

Yes, I would black box a PC (no updates) running a stable and free HMI, then for I/O the options are generally less expensive.

Another player in the PC basedHMI market that has been the subject of a recent thread:
http://www.peakhmi.com/

So, this is probably the first time I can say that I recommend investigating low cost efficient ethernet/IP I/O, or a multichannel thermocouple module on USB to a local PC. It can be remotely monitored and be wired for safety if the PC should crash.

Yep, a $400 PC Wearing Archie-Ware and a USB datalogger for i/o. It will be ab educational challenge but you came to the right place for that (education).



Welcome to the forum.
Paul

 

[danw]

A couple of observations:

A lot of the single loopers have some digital communication option (typically 2 wire RS-485) and some of them came out with a Windows program at one time or another that could download a configuration or act as a simple HMI. What about upgrading to comm and a vendor program with your current devices?

A PLC with T/C inputs sounds viable. I would expect the vendor to answer how many PID loops it is expected to handle.

The single loop PID controller typically does 2-4 updates per second. That's about 10,000 times faster than need be for room temperature control. Even if any given device's PID was limited to once or twice or 3 times a minute updates, so what? I suspect AD or any vendor could answer how many PID loops are supported. A commercial PACs (multiloop PID controller that looks like a PLC), like Honeywll's, say outright "2 scans per second", 64 PID loops before any effect on scan time."

Have fun looking for an inexpensive HMI. Single loopers continue to survive in the market place because each one comes with its own HMI that shows the temperature.

There's that other really inexpensive mail order house, Ezautomation, that you could look at.
http://www.ezautomation.net/products/ezplc.php

 

[Lancie1]

I am worry of a failure in the PLC program, or some other device, but it's not different than what I am using right now.

To make it fail-safe, consider using relays or manual selector switches on the PID outputs. When the relays are de-energized, a connection to a manual switch is automatic and if PLC fails, you can use the manual switch to apply emergency heat.

 

[KalleOlsen]

Hi JNT!

Ad using a PC for controlling: Here's the link to Archie's Twincat quick start on Youtube.
http://www.youtube.com/watch?v=l_nFE9wx8OM&playnext=1&list=PLBF6147FAFC3665BA

Kalle

 

[Peter Nachtwey]

I am going to ask a Tom Jenkins type of question. Why not use a simple on-off thermostat?

 

[JNTurcotte]

I am going to ask a Tom Jenkins type of question. Why not use a simple on-off thermostat?

Actually I am using proportional thermostat.
I also need to have the possibility of adjusting the temperature lower for nights and have variation depending on the season for breeding.

The on/off thermostats works, but they have more "overshoot" troubles.

Neither does the on/off or proportional units, give me feedback in case something is going wrong.
I also don't have the flexibility of controling other units in the room (ventillation, AC fan, lights, etc...).

I also hopping that this could help me save some money.

Each zone control up to 4 snake accurately, if I had more, it's less reliable and have more fluctuation. So my expense is actually around 25-35$ in snake for the control.


But I am realizing that it's probably the less expensive and less troubles to keep it with a proportional thermostat so far.
But I have to let go the temperature data log if I go with that situation.

Otherwise, might have to build a PLC that act as a proportional thermostat instead, might be cheaper.
I still don't know how to do this. I would need to have analog output, but no PLC can give out 3 amps, 120v, per output. A mechanical relay on/off system wouldn't last long that way.

 

[OkiePC]

I still don't know how to do this. I would need to have analog output, but no PLC can give out 3 amps, 120v, per output. A mechanical relay on/off system wouldn't last long that way.

You can use PLC relay outputs that can handle about 500,000 on/off cycles up to 5 amps, but I would opt for cheaper DC outputs that switch individual (cheap) ice cube relays good for about the same number of cycles, but easy to replace if one contact should fail.

A PLC analog output is typically 0-10vdc or 0-20mA current. This is not how you'd drive 120vac 3 amp heaters. Relays or solid state relays would be your only option for that, nto analog.

Analog outputs could be used to send a proportional command to a variable speed drive (fans, pumps) or a damper positioner for your application, if you need those types of controls.

Make a list of the devices you want to control with on/off signals and include voltage and current requirements of each.

 

[ddnnis]

Try the Watlow RMC, this is an awesome loop module that can be configured for numerous loops. It also has a lot of comm's options available.

 

[Peter Nachtwey]

The on/off thermostats works, but they have more "overshoot" troubles.

That is because simple thermostats work simply off the error and not the error rate too like a PID or Sliding Mode Control.
To get a good error rate you need feed back with fine resolution and an even sampling interval.

Otherwise, might have to build a PLC that act as a proportional thermostat instead, might be cheaper.
I still don't know how to do this. I would need to have analog output, but no PLC can give out 3 amps, 120v, per output.

No. If you can simply turn the heaters on and off with a simple relay and you want a solid state relay. If you turn the heaters on and off fast enough the control output will be effectively like a analog signal but instead of outputing a value like 756% of full on you have the heater on for 75% of the time. I would be looking at using sliding mode control, SMC. SMC is basic on-off control with a rate term. The trick will be getting fine resolution feed back or doing an over sample and filtering to compute an accurate rate of change in error or PV.

Error=SP-PV
ErrorRate=ErrorRateFunction(?)  // I have several ways of doing this.
If Error+Tau*ErrorRate > 0 THEN
  HEATER_ON
ELSE
  HEATER_OFF
END_IF

Where tau is a time constant and the only parameter that needs to be tuned.

 

[keithkyll]

I found out about AutomationDirect 05 and 06 models, but I am worry that they can't have enough PID running at the same time and that the number of thermocouples input cards are low...
I would like to add an HMI to make modification on the temperatures and testing. But can't seem to find a basic hmi for a reasonable price...
If anyone could point me to a cheap PLC with PID and thermocouple solution, I would appreciate.
And some cheap HMI solution, it would be even better...

I'll try this again.
I've done 6 PID'S on a DL260 with excellent results. The DL06 has the same processor.
You need to pulse SSR's. Read page 8-68 of the DL06 manual to how to do this. You don't need high speed outputs.
Size the SSR 3.5x current to handle cold start surge.
D0-06DD1
F0-04THM
SSR Magnecraft 12 Amp

That will cost about $100.00 per channel. HMI and thermocouples are additional.
The USB datalogger and other PC based options are also good choices, but costs just as much if you're buying new. I have many reasons for not liking PC based control. Windows lockups, boot time, etc.
In all cases, you also need a UPS that has enough reserve to drive heaters. That will be another $2000.00 for 30 minutes to 1 hour reserve.
With that setup, you can sleep at night. After about 2-3 years, you'll need to replace UPS batteries. Other than that, everything else will run almost forever.

 

[JNTurcotte]

I understand the pulse PID stuff without problem, I have been using it.
Just wasn't aware that price of SSR dropped that low. It's still more expensive but not bad for it's use as far as it doesn't generate too much heat.

As for expense using a D06 PLC with 8 PID (as stated from them) :
D0-06DD1 DL06 20 DC IN/16 DC SINK OUT MICRO PLC W/AC P/S $239.00
F0-04THM 4 CHANNEL THERMOCOUPLE OR 16-BIT MV INPUT $199.00 X 2 = 398$
H0-ECOM100 10/100MBIT ETHERNET COMMUNICATION MODULE DL05/06 OPTION MODULE WITH MODBUS TCP $199.00
Solid State Relays 70S2-N SSR : 18.48$ x 8 = 147.84

Total : 983.84$ or 122.98$/zone
Without the thermocouples and without an HMI module.

It's still quite expensive.
The thermocouples cards are not cheap, neither the ethernet module (but it might not be necessary, I think it's possible to use a rs232 to ethernet converter, but not sure if it would work for what I want to do).
I know I could use some signal converter for the thermocouples, but I don't think it would be less expensive.