Ohm\u2019s law is the very foundation of how Building Automation and Energy Management get done. The simple relationship of Voltage, Current, and Resistance makes controlling a building with a computer possible. \u00a0Ohm\u2019s Law is stated as:
\nV=I X R<\/p>\n
I=V\/R<\/p>\n
R=V\/I<\/p>\n
V=voltage expressed in Volts<\/p>\n
I = current expressed in Amps (note that 1000 milliamps = 1 Amp or 1 mA = 0.001A)<\/p>\n
R = resistance expressed in Ohms
\nOne common use of Ohm\u2019s Law is signal conversion. Using a 4-20mA signal to operate a device controlled by a 2-10V signal is a fairly common occurrence in Building Automation and Energy Management. \u00a0Here is how it works:<\/p>\n
V=I X R<\/p>\n
V = 4 mA X 500\u03a9<\/p>\n
V= 2<\/p>\n
V=I X R<\/p>\n
V = 20 mA X 500\u03a9<\/p>\n
V = 10<\/p>\n
Applying a 500\u03a9 resistor in parallel to a 4-20 mA signal creates a 2 \u2013 10 Volt control signal. \u00a0Here is a wiring diagram from a direct-coupled actuator that uses this:<\/p>\n
![\"diagram\"](\"https:\/\/assets.kele.com\/content\/wp-content\/uploads\/2013\/02\/51aab10e-6e0f-439a-a750-60075c75f663.jpg\" "\\"diagram\\"")
<\/p>\n
<\/p>\n
Another application to consider is how does a Building Automation or Energy Management system sense temperature? Ohm\u2019s Law, that\u2019s how. Thermistors and RTDs are devices that have resistances that change with temperature. Since resistance can be calculated by applying known voltage and current values, computers can \u201csense\u201d temperature using Ohm\u2019s Law (R = V\/I). Once the resistance is known the temperature can be associated via either a calculation or look up table.<\/p>\n
![\"temp](\"https:\/\/assets.kele.com\/content\/wp-content\/uploads\/2013\/02\/ac1560bb-e6f8-4ecc-8781-3c2494328a4e.jpg\" "\\"temp")
<\/p>\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
If there were an awards show for Building Automation and Energy Management; there would have to be a lifetime achievement award. All awards shows have them. For Building Automation and Energy Management there may be none more deserving than Ohm\u2019s Law. Ohm\u2019s law may be the Beatles of Building Automation and Energy Management. The influence […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[2,7],"tags":[30,32,95],"class_list":["post-471","post","type-post","status-publish","format-standard","hentry","category-back-to-basics","category-kele-makes-it-easy","tag-back-to-basics-2","tag-basics","tag-ohms-law"],"acf":[],"yoast_head":"\r\n