Beer Brewing machine

[cateid 0]

Hi,

i'm planning on building a AIO electric beer brewer with about 80 liter capacity. i was thinking of using an micro 850 i have for controlling mashing stages, circulation pumps, temp controll.

i was thinking of using two 1600w heating elements and a 24vDC pump. 

My I/O options are 14/10 (micro 850 lc-50 24qwb) only relay outputs, an analog input plugin with 4 inputs and an analog output plug in with 2 outputs.

since i cannot run any SSR directly from the PLC because of the relay outputs, what can i ad to best control the heating elements? it requires accurate temp controlling within +- 0,5 degree. 

Also, what would be the best solutuion to controlling the pump?

i have an 7" TFT HMI from AB i was planning on using for set values, temp readings, timers etc. and ofc some awesome graphic simulation of the system. 

BRGDS Cato

[ElectronGuru 81]

For the heaters, assuming you want variable temperature control, you could use an SCR (or similar) heater controller that takes a 0-10VDC or 4-20ma input signal. Just run the heater control input from a PLC analog output. You would have to add an I/O expansion module, like the 2085-OF4.

You mentioned that the pump motor is 24VDC. This leads me to believe that it's a constant speed motor, yes? If so, most Allen Bradley PLC output relays can handle up to 2 amps each, but check the output spec on yours before wiring anything up. Most controls engineers don't like doing this because inductive loads (like motors) tend to produce a lot of electronic noise (EMI) in the control circuits, and this could interfere with your heater control or the PLC itself, every time the motor starts & stops. If you don't have a lot of I/O and it's a small enough motor, this method might not be an issue and could be a way to keep costs down. Otherwise, it's far more common to use the PLC relay output to pilot a heavier, motor starter relay that's wired directly to the motor. 

Hope this helps.

[cateid 0]

Yes variable temp is a must. wont an SCR generate noise? could a solution be to run 0-10v to an PMW "generator" wich in turns controls an SSR?

i already have an analog output: 2080-OF2.

The pump is variable speed.

[ElectronGuru 81]

Most modern SCR controllers have noise suppression built into them. Among other things, I've used them for controlling infrared welders. We vary the volts and current to an IR bulb array via the SCR controller, which takes it's 0-10VDC pilot signal directly from a ControlLogix analog output. The feedback loop there is current, rather than temp, but the principle is exactly the same; closed loop temperature control by varying current to the heater. Here's a link to the vendor we used for that project:

https://www.heraeus.com/us/hng/products_and_solutions/heraeus_noblelight_america/infrared_controls_1/scr_controls.html

On the other hand, if your heater elements are AC and can handle a variable frequency without burning up, you could just wire the heaters directly to a PWM driver. I'd shop this around to find the most reliable and cost-effective method for your process. Heraeus is a temperature control company, so they'll have lots of options but as I recall, they're a bit expensive. You might also ask an application or field engineer at your local Rockwell distributor for input on this.

What is the HP & amps on the motor? With the motor being only 24VDC, it's hard to imagine you're pulling a lot of current. If the pump motor is within the current rating of the PLC analog output, just use one of the analog outputs to control its speed. Otherwise, you'll need to use the PLC analog output to signal a motor controller (like a DC drive or motor control transducer) to vary motor speed. 

[BobLfoot 301]

Just my two cents having "fought" with micro 850's on our washer units, If you can afford it, use a CompactLogix instead.  They're much more robust than the Milton Bradley Micro 850 Toy PLC.  I'd hate for you to lose a batch of brew due to an 850 crashing.  Just my two cents.  

[ElectronGuru 81]

That's more like $1.25, BobLfoot! The Micro800s were introduced by Allen Bradley to compete with companies like Automation Direct, who make cheap, throw-away PLCs. The 800s are pretty reliable hardware but the programming tool, CCW, is not the most user-friendly software I've used. I'd take a Compact- or ControlLogix any day, but not everyone can afford the hardware and the programming Studio is quite expensive. A better option for most people is the MicroLogix 1100 or 1400 but then you have to spend upwards of $2,000 for the programming tool. It all boils down to getting what you pay for.

[cateid 0]

hehe, my idea was to save money on this project, and since i have this micro850 laying around from a school project i figure why not use it for something.

i think i will get an plug in module with transistor output to controll two SSR's and use a PWM block controlled by the PID block with max 1 min cycle time , and a DC drive with 0-10v input for the pump. the pump is only about 50 watts. 

[Joe E. 259]

Unless AB has changed something, the MicroLogix 1000 (serial only) and 1100 (serial & Ethernet) can be programmed using the free version of RSLogix 500. The ML1100 supports the 1762 family of expansion modules, so that should do what you need it to. Won't be as cheap up front as using the 850 you have laying around but I wouldn't be surprised if it ends up costing you less in the long run with development time and failures.