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Temperature measurement using PT100 sensor

Created by: xmxbx at: 4/26/2006 4:36 PM (3 Replies)

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4/26/2006 4:36 PM	Rate (0)
xmxbx Posts: 2 Rating: (0)	Hallo, I'd like to control the temperature in a water tank using a PT100 sensor. I already have the PT100 module for LOGO!. I need to activate a refrigerator if the temperature > max.temp (f.e. 28°C) and to activate an heater if the temperature < min.temp. (f.e. 25°C). Do I need to use 2 analog inputs, or could I use only one input, programming the min. and max. checks on the same input? Thanks a lot. Bye, Marco
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4/27/2006 4:52 PM	Rate (1)
Fux Posts: 661 Rating: (123)	Hello xmxbx, only one analog input should be enough. Here i´d like to show you a very simple way: Attachment PT100.zip (1061 Downloads)
Fux Posts: 661 Rating: (123)
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4/27/2006 5:51 PM	Rate (0)
xmxbx Posts: 2 Rating: (0)	[quote user="Fux"]Hello xmxbx, only one analog input should be enough. Here i´d like to show you a very simple way: Hi Fux, thanks for your help, but I'm not sure that it work as I want. From you example I understand: - when the temperature > 27.9°C the Refrigerator is turned on, but also the Heating is turned on bucause the same signal is in AND with 'high'. Is it correct? Thanks a lot. Marco.
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5/2/2006 10:40 AM	Rate (1)
Fux Posts: 661 Rating: (123)	If you simulate, you will see that the „high“-signal only reaches the output Q2 if the output of the analog threshold trigger is “low”. If the value of the analog input is > 279, the output of the analog threshold trigger is “high”. From this time the refrigerator is activated. At the same time the heating is turned off (because the “high”-signal of the analog threshold trigger is connected with a negatived input of the “AND”). That means: If the analog value >279 ->> Q1 is active, for so long until the analog value <251, then Q2 is active. So only one output is activated at the same time. Is that you thought about? Greetings Fux
Fux Posts: 661 Rating: (123)
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