Small knowledge of instrument and meter bridge

It is understood that a bridge is a tool used to measure a variety of quantities, such as resistance, inductance, capacitance, etc. And the bridge is a circuit composed of four branches, so each branch is called the "arm" of the bridge. So what little knowledge about the bridge? Here's a simple talk.



The use of single arm bridge:



1, the first open lock galvanometer (inside and outside), adjusting the zero pointer is transferred to the zero.



2, the measured resistance is attached to the position of "".



It is required to use a relatively short connecting wire and clean the film. The joint is tightened and the clamp is avoided. Because of bad connections will make the balance of the bridge is not stable, which may damage the galvanometer.



3. Estimate the size of the measured resistance and select the appropriate bridge arm ratio so that the four gear of the comparison arm can be fully utilized. It is easy to balance the bridge and ensure the 4 effective numbers of the measurement results.



4, first press the power button to B (lock), and then press the G button (galvanometer pick).



5, the adjustment arm resistance galvanometer point zero, bridge balance. If the pointer refers to "+", the comparison arm resistance is added, the needle points to "-" and the comparison arm resistance should be reduced.



6. Read the data: the arm ratio arm = the measured resistance



7, after the measurement, disconnect the galvanometer in button, disconnect the power button, and then remove the measured resistance, then the galvanometer lock button, to prevent damage in the process of moving the galvanometer.



The values of R2, R3 and R4 are adjusted through the bridge. When the bridge is balanced, there are R1=R2 x (R3/R4) so that the measured resistance can be measured. It can be seen from the picture: R1 measured resistance includes lead resistance and contact surface contact resistance, so the actual resistance and contact resistance should contact resistance minus the lead, the measured resistance is smaller, the lead error increases, so the Wheatstone bridge is used to measure the resistance of more than 1 in Europe, the general process for 1~99990 euro. For switches, the contact resistance is generally in the micro European level, so it is not suitable to use this bridge. Because the lead resistance is millieu level, it cannot be measured, so we can use double arm electric bridge.