Scaling in C-More

[Eric Nelson]

Just got back from my customer. Turns out his customer was okay with him using a thermometer that reads °C directly in that tank, so I didn't have to make the temporary change after all.

I'm going to proceed with Bernie's idea and make a toggle between F and C for all tanks, and download it later in the week.

Thanks again for all the help guys! :site:



-Eric

 

[Eric Nelson]

I just spent the last 2 hours duplicating all the objects relating to temperature (setpoints and displays), scaling them, and overlapping onto the existing objects. While there were a LOT of screens. it was pretty easy to just copy/paste the screen, delete non-temp stuff, edit the scale, limits, and visibility, then copy/paste them back over the existing screens. I then made the existing objects hide when °C is selected. Using the simulator, everything works great!

The last thing I'm trying to wrap my head around is the alarm settings. They have separate high and low alarm limits, but they are based on offsets from the setpoints, not a fixed temperature In other words, lets say you set the high alarm for 10°. If the setpoint is 100°, then the alarm will trigger at 110°. If the setpoint is 150°, the alarm triggers at 160°.

In this case, I can't use the same '32 to 212 = 0 to 100' scaling method. Zero offset in °F would end up being -17.8°C, NOT zero. I think I want to set the scaling like I show in the attached screenshot, but just want confirmation before I edit 80 alarms.

I must be getting old...



-Eric

 

[Eric Nelson]

Yeah, this alarm scaling is NOT going to work. Sure, 50°F is 10°C, but 25°F is NOT 5°C.

Looks to me like I can only add/subtract a fixed value to the 'already converted' temperature unit. Am I stuck doing the alarm scaling in the PLC?



-Eric

 

[Steve Bailey]

The scaling for an offset is Degrees C = Degrees F * (5/9)

Think of it this way. The Fahrenheit scale divides the temperature difference between the freezing and boiling points of water into 180 units (212 - 32). The Celsius scale divides the same span into 100 units. So 1.8 units in the Fahrenheit scale is the same "distance" as 1 unit in Celsius.

 

[Eric Nelson]

So 1.8 units in the Fahrenheit scale is the same "distance" as 1 unit in Celsius.

So, if I make my scale 0 to 18 = 0 to 10, it should be correct? EDIT: Apparently, yes!

Forgive me, it's been a looong day



-Eric