The difference between zero adjustment and zero elimination in power analyzer

There are two functions in the power analyzer: zero adjustment and null elimination (NULL). They are both used to adjust the measured value. Users often don't know how to choose. What is the connection and difference between them? Let's get to know the different application scenarios of these two functions. 
1. Zero adjustment Before using the measuring instrument, you need to perform zero adjustment. Zero adjustment is to instruct the input signal in the internal circuit of the PA8000 high-precision power analyzer to be zero, thereby improving the accuracy of the instrument's measurement. There are two zero adjustment methods: automatic zero adjustment and manual zero adjustment. Zero adjustment refers to the function of creating a state where the input signal is zero through the internal circuit of the PA8000 and setting the current level to zero level. In the measurement menu shown in Figure 1, the user can configure the automatic zero adjustment switch. If the automatic zero adjustment is turned on, the instrument will automatically perform zero adjustment after changing the measurement range and input filter; if the same measurement range and input filter are used for a long time, the zero level of the PA8000 high-precision power analyzer may change due to changes in the surrounding environment. In this case, manual zero adjustment must be performed. Tip: For accurate measurement, it is recommended to let the instrument warm up for more than 30 minutes before performing zero adjustment. In addition, the ambient temperature must be stable within the specification range. If the measurement range and input filter remain unchanged for a long time, the zero level will also change after the ambient environment of the PA8000 changes. In this case, it is recommended to perform zero adjustment.   
Figure 1 Zero adjustment setting 2. Zero elimination (NULL) When the instrument is connected to an external sensor or test lead, the NULL function can be used to subtract the bias voltage, that is, to remove the DC component in the measured signal. Please execute the NULL function in the no input state (current input terminal open, voltage input terminal short circuit). When the NULL function is set to ON, the NULL value is set to the previously measured Udc and Idc (numeric data of simple average of voltage/current), Speed ​​and Torque (when the motor card function is installed and the input signal of the sensor is an analog signal). If the previously measured Udc and Idc, Speed ​​and Torque do not exist, such as turning on the power and the NULL function without performing measurement, Udc and Idc will be set to "0". The setting of the NULL function is shown in Figure 2. Tip: Changing the range, external sensor ratio, or filter setting will automatically release the NULL function. If you perform the steps to release the NULL function in the hold state, the NULL function will be automatically released when the hold is released or a single measurement is performed, and the NULL indicator will go out. 
 
Figure 2 NULL setting