newtry zx21 decade resistance box adjustable lab rotary resistor substitution box precision dc variable knob switch 0 to 99.9999kr 0.25w newtry zx21 series rotary resistance box for the dc circuit for use adjustable resistance, has a lower value of zero resistance, are all the most commonly used laboratory instruments for schools, factories and research units for electrical measurements and other experiments.<br><br>when you test with the item, please make sure the voltage is under 5v, and the current is under 50 ma. <br> the power is 0.25w<br> <br><b>major performances </b><br> made of high quality manganese copper wire, the resistance value does not change with the temperature, so that the resistance box is more accurate.<br> with high quality metal film resistors, it is more expensive than carbon film resistor, but it has good stability, little influence on temperature and high accuracy.<br> better use knob switch designed according to customer needs<br><br> <b>note:</b><br> 1.when the proper use of resistance box to rotate the knob in each group, so that the contact resistance is stable and reliable.<br> 2. the maximum allowable current value of the resistance box in use should never exceed the specified.<br> 3. when only a small change in resistance, then wire to the "0" and another small indication terminal, can reduce the resistance inside the lead resistance.<br> 4.the resistance box should be placed in shelter room, the air temperature +10°c~ + 40°c , relative humidity below 80%, should not contain harmful impurities which can cause corrosion.<br><br> <b>attention: </b><br> we will send the product to you as soon as possible <br> if you have any questions , please feel free to contact us <br>