{"id":2017,"date":"2017-02-08T19:44:22","date_gmt":"2017-02-09T03:44:22","guid":{"rendered":""},"modified":"-0001-11-30T00:00:00","modified_gmt":"-0001-11-30T07:00:00","slug":"2017","status":"publish","type":"post","link":"https:\/\/www.vernier.com\/til\/2017","title":{"rendered":"An experiment using the current sensor of the power amplifier (PAMP) gives unexpected results"},"content":{"rendered":"<p>The output of the Vernier <a href=\"\/product\/power-amplifier\/\">Power Amplifier<\/a> (<nobr>PAMP<\/nobr>), is bipolar. The negative terminal is not quite at ground, because of the presence of a small current sense resistor. Current through this resistor is used to report the current delivered to the PAMP load. <\/p>\n<p>Per the documentation that comes with the PAMP, the current readings will be correct only if no other point in the circuit is grounded. <\/p>\n<p>This means that one must use great caution when measuring potentials in the load circuit. The <a href=\"\/product\/voltage-probe\/\">Voltage Probe<\/a> (<nobr>VP-BTA<\/nobr>), is a poor choice because the black terminal is grounded to the interface. Instead, one should use the <a href=\"\/product\/differential-voltage-probe\/\">Differential Voltage Probe<\/a> (<nobr>DVP-BTA<\/nobr>), or <a href=\"\/product\/go-direct-voltage-probe\/\">Go Direct<sup>&reg;<\/sup> Voltage Probe<\/a> (<nobr>GDX-VOLT<\/nobr>), because its leads are floating.<\/p>\n<p>For example, consider a very simple Ohm&#8217;s law experiment. Connect a 10 &Omega; resistor across the output terminals of the PAMP. Connect the VP-BTA across the resistor, black lead on the black terminal of the PAMP. <\/p>\n<p>Connect the PAMP current output to a LabQuest. Connect the VP-BTA to the LabQuest. Both will be detected by the LabQuest App. Zero both sensors. Configure a selected events data collection run. Use the Power Amp application to set the output potential to a variety of values, keeping the current and voltage readings each time. <\/p>\n<p>Now graph potential <i>vs<\/i>. current. The slope should be the resistance. You&#8217;ll get about 12 &Omega;, instead of 10, because not all of the current returned through the sense resistor. Instead, some current returned through the black lead of the VP-BTA. This configuration will never work because of the bipolar, non-differential nature of the VP-BTA. <\/p>\n<p>The experiment works as expected with the DVP-BTA or GDX-VOLT.<\/p>","protected":false},"excerpt":{"rendered":"<p>The output of the Vernier , is bipolar. The negative terminal is not quite at ground, because of the presence of a small current sense&#8230;<\/p>\n","protected":false},"author":100811,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[],"tags":[1010,1014,3228,1652,1466,210],"class_list":["post-2017","post","type-post","status-publish","format-standard","hentry","tag-dvp-bta","tag-gdx-volt","tag-ohm-ohms-law","tag-pamp","tag-power-amplifier","tag-vp-bta"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/posts\/2017","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/users\/100811"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/comments?post=2017"}],"version-history":[{"count":0,"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/posts\/2017\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/media?parent=2017"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/categories?post=2017"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vernier.com\/til\/wp-json\/wp\/v2\/tags?post=2017"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}