Created Date: April 07,2015

Created by: ControlsGuy

1) Agree. Never drive a power load with a transistor output. Either get a relay output module (fine) or (better) drive a relay with a transistor output, and control the valve with the relay.

2) Positive logic (positive -> switch -> load -> negative) is DEFINITELY better than negative logic (assuming you 're grounding the negative as is normal practice). For outputs this is pretty uniformly called sourcing, but inputs are a little tricky. Some brands use "sourcing " as a synonym for "positive logic ", which is what you should use, while some brands (AB notably), call it sinking, because the input is actually sinking when used in a positive logic circuit.

Why is positive logic correct? Not only is it the US and European standard, it just makes more sense unless you 're the type person who puts light switches in the neutral leg instead of the hot (no one does that). Stuff should not read true if it becomes accidentally grounded. Motors should not start because someone ran into a metal conduit with a forklift. Not the best idea someone ever came up with.

Created Date: April 07,2015

Created by: Tinker

One thing to find out is what is the control input on your valve actually doing, since there is a power connection to the red wire, which presumably handles the ~500mA motor current, it is possible the green control terminal is very low current, but it is also possible that it too can have around 500mA, in the latter case you would need an interposing relay, but in the former you may not.

While controls guy made a reasonable augment for sourcing outputs, there used to be a good argument for sinking transistor outputs in that NPN transistors were easier to make (cheaper) and available in higher power ratings, now that most things use MOSFETs the difference is not so great, but it is still easier to turn on a low side (sinking) device. If you don't turn on a MOSFET switch HARD, the magic smoke can get out, but that is the device designers problem, not yours.

Created Date: April 08,2015

Created by: pretender_2002

Ok, I think I understand why positive logic is generally the better way to go. Essentially for an output if the switch is after the load (i.e. positive>load>switch), there is a chance there is a short in the system and the output turns on when the switch is still off. However, putting the switch in front of the load means that if there is a short in the system when the switch is off the load will not power on (i.e. the current will short to ground before the switch which is inherently before the load). To me this also sounds preferable and I will proceed with the valves that use positive logic and a sourcing output module for the click. Thanks for the input.

Created Date: April 16,2015

Created by: Herman

Hm, I wouldn't connect the DC negative to ground, because it will introduce noise in your system. When I learned to put control panels together, they told me to keep the DC wiring strictly separate from the ground (and all other AC related wiring of course).

Then, the concern of something DC accidently getting connected to ground becomes just as moot as something DC accidentally getting connected to anything else.

Created Date: April 23,2015

Created by: KB1GNI

On the other hand, I learned early on that it was best not to float your DC power supply for a couple of reasons. If you have any analog inputs, a floating zero volts will cause the signal to drift around. Not referencing the zero volts to ground also makes troubleshooting for the back shift maintenance guys a little more difficult, which can lead to late-night phone calls.

I never had any issues with noise on anything where we grounded the zero volt DC. Your Mileage May Vary, of course.

Only other thing I'd add would be to use diodes or Varistors across the motor on the ball valve, depending on if it is DC or AC. The back EMF will shorten the lifespan of the relay contacts considerably, even if it is a small motor.

Created Date: April 05,2015

Created by: pretender_2002

I am working on putting together an automated home brewery using the click plc.

The plan is to use the click to drive solo 4848 controllers, read a couple of analog pressure sensors (for volume sensing), drive a couple of VFDs (GS1 drives controlling 1/4 hp motors) and to operate approximately 12 motorized valves (24VDC, see link for similar valves).

http://www.flow-controls.com/2-way-Motorized-ball-valve-CWX-15Q-N-81.html

I have most of the parts that I need and I have tested most everything (I am communicating with the Solo controllers and GS1 drives using MODBUS). I am not an engineer of any sort, but the wiring for everything aside from the valve was very straightforward. I am still learning some of the ladder logic programming but I don't think that will be to much of a problem.

I thought I understood the sourcing vs. sinking concept, but I wanted to get some feedback from others to make sure my understanding of the wiring is correct.

The few questions I have are:

1. The valves are very low power and as I understand it the outputs should be able to provide enough power without using relays (0.1 amps per point), but I would like to verify that this should work as I do not want the system to get to complex.

2. I had purchased a valve with "CR7 01 " wiring see the diagram below, there are other wiring options however as I understand it this one should be the appropriate one (i.e. the other valve diagrams either would not work with a single plc output or they use a spring to close the valve which decreases the life of the valve). When the switch is on the green wire is connected to negative and the valve closes, conversely when green is not connected the valve is powered open. It appears to me that I should be using a sinking output module (i.e. C0-16TD1) with the power supply negative connected to C1 or C2, then the valves red wire connected to the positive wire on the power supply, lastly the green wire connected to one of the outputs (i.e. Y101) and the black wire connected to negative wire from the power supply. All of the other wires on the valve provide signal feedback for whether the valve is open or closed (i.e. I am not too concerned with that just yet). The way I understand it is that the PLC will be the switch in the diagram that turns on and off the sinking/negative connection.

http://www.china-tonhe.com/upload/Image/%E7%BA%BF%E8%B7%AF%E5%9B%BE/CR701%E7%BA%BF%E8%B7%AF%E5%9B%BE.jpg

3. I can also use a slightly different valve wiring "CR7 03 " which is essentially the same however the green wire switches with the positive instead (see link below for all of the wiring options, there are several different valves out there that are all very similar). In this case I believe I would just switch to a sourcing output module, correct? Is there a preference to sourcing vs. sinking outputs?

http://www.china-tonhe.com/Products/Electric_ball_valve/T25_Series_Electric_Valve/T25-S2-B_Motor_control_valve/T25-S2-B_Motorized_ball_valve_539.html