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--- projects:anemometer [2023/10/03 15:20] – [Calculating wind speed] jattie
+++ projects:anemometer [2024/02/18 19:54] (current) – [Important notes about reed switches] jattie
@@ Line 80: / Line 80: @@
 Remember to replace ''pin_number'' with the desired GPIO pin number for your application.
+===== Important notes about reed switches =====
+The  sensitivity of a REED switch is characterized by the value of the magnetic field which is required to
+change its state. The magnetic field is expressed in Ampere-turns  (or ampere/meter). In order to close a normally open switch, for instance, a certain number of Ampere-turns, called **CAT**, are required (**c**losing **A**mpere-**t**urns). To open the same switch the magnetic field must be reduced down to an **o**pening value in **A**mpere-**t**urns **OAT**).
+<WRAP center round tip 60%>
+OAT<CAT is always true
+</WRAP>
+Order of magnitude OAT-CAT :
+^For standard switches^^
+|CAT |12 and 50 Ampere-turns|
+|OAT |5 and 30 Ampere-turns|.
+^For standard or mercury wetted switches^^
+|CAT |35 and 150 Ampere-turns|
+|OAT |10 and 80|
+<WRAP center round important 60%>
+NOTE : if the leads on a switch are cut, the CAT and  OAT values will increase
+Bending modifies the CAT and OAT values of a switch
+Cutting the leads on a REED switch has the effect of increasing the CAT and OAT ratings in a significant manner.
+</WRAP>
+The figure below illustrates this variation.
+{{:projects:screenshot_2024-02-18_195106.png?400|}}
+===== Reed Reference Documents =====
+  * {{:projects:ap-interen.pdf|}}
+  * {{:projects:notes_reed_switch_modifications.pdf|}}