Editing Comparator (section)

===Null detectors===
A null detector identifies when a given value is zero. Comparators are ideal for null detection comparison measurements, since they are equivalent to a very high gain amplifier with well-balanced inputs and controlled output limits. The null detector circuit compares two input voltages: an unknown voltage and a reference voltage, usually referred to as v<sub>u</sub> and v<sub>r</sub>. The reference voltage is usually on the non-inverting input (+), while the unknown voltage is usually on the inverting input (&minus;). (A circuit diagram would display the inputs according to their sign with respect to the output when a particular input is greater than the other.)  Unless the inputs are nearly equal (see below), the output is either positive or negative, for example ±12&nbsp;V. In the case of a null detector the aim is to detect when the input voltages are nearly equal, which gives the value of the unknown voltage since the reference voltage is known.

When using a comparator as a null detector, accuracy is limited; an output of zero is given whenever the magnitude of the voltage difference multiplied by the gain of the amplifier is within the voltage limits. For example, if the gain is 10<sup>6</sup>, and the voltage limits are ±6&nbsp;V, then an output of zero will be given if the voltage difference is less than 6&nbsp;μV. One could refer to this as a fundamental uncertainty in the measurement.<ref>{{cite book |title=Electronics and Instrumentation for Scientists |last1=Malmstadt |first1=Howard V. |last2=Enke |first2=Christie G. |last3=Crouch |first3=Stanley R. |publisher=The Benjamin/Cummings Publishing Co |year=1981 |isbn=978-0-8053-6917-5 |pages=[https://archive.org/details/electronicsinstr0000malm/page/108 108–110] |url-access=registration |url=https://archive.org/details/electronicsinstr0000malm}}</ref>