Control a timer (or any variable) with a dial/pot?

Hello all,

I am writing a logic file and I have a need to allow an operator to change the length of a timer. I am using a micrologix processor with 2 analog inputs. Is it possible to use an analog input to grab a value from a dial or pot adjuster? What is the simplest way to accomplish this task?

Thanks in advance

You can take the analog value and scale it from min to your max time put it in the preset time and your good to go.

Dependant on your Micrologix you are using, some models (ML1500 & ML1200) have an inbuilt user adjustable pot that you can assign to whatever you want.
They are under one of the covers/flaps on the front of the unit. (called trimpots)
If it is an 1100 then you can use the LCD to do what you want.

Re-read the post and from the description of 2 analog inputs it is an 1100. Search the AB website for the manual on the LCD for this model.

Regards Alan Case

A $129 alternative: http://www.optimate.com/products/optimate/413.html

Yes you can use a dial or a pot but it is a bit ugly and imprecise. The analogue input sees a voltage, often between 0 and 10 volts and converts that voltage into a number, the range of number depends on the PLC and analogue units you are using. You probably won't have a 10V supply available so you will have to use a resistor in series with the pot to drop 14V of the 24V that you will have available. The ugly and imprecise bit comes in because if you set say 5 on the pot you won't always get exactly the same voltage output so it depends on the accuracy you need. As Alaric shows a much better soltion would be a small HMI, you set 5 on the HMI and the PLC will always see 5. Only problem is that $129 is $129 and can your job stand that cost.

Bryan

Whatever method you end up using, I'd advise you do not go directly to the timer .PRE (Preset) value.

Go to an intermediate register, and then make sure it's within limits before passing it on to the timer's .PRE word.

Using an analog input for example, you might actually get a negative number. Negative presets will generally fault out the processor, not good, so clamp the desired preset to some predefined min/max limits.

Thanks for the advice guys. Ill look into an external device.

Put clamping statements on the intermediate register. If less than zero, move zero and so forth.
You will probably have to use a linear pot

Is there a reason to stick with a trimpot or potent at all? Why not an up/down PB and one shot an add/sub to the preset of the timer? Just a thought.

I would suggest that with touch panels being under $200 you look at that option. You would also gain access to all kinds of alarm and diagnostic capabilities.

http://web5.automationdirect.com/ad...o-Graphic_Panels_-a-_Keypad_Bezels_(all_types)

How about a thumbwheel and BCD? Ops can thumb in a time 0-9 per register and the decimal equivalent can be moved to the timer preset. I don't know what resolution you are needing, but I think it would be difficult to get a settling value from a variable pot.