Explain the knowledge of precision resistance, take it away.

Precision resistor are resistor with higher accuracy and lower temperature drift. In addition to the basic requirements of high precision, extremely low temperature drift, extremely high reliability and stability are required, and stable performance is a prerequisite for high-quality standard resistor.

1. Temperature drift characteristics

Standard resistance materials with good performance, such as manganese copper or nickel-chromium alloy, have a very low temperature coefficient, which can reach less than 1 ppm/°C at room temperature. When the room temperature fluctuation is less than 0.01°C, the resistance value is measured due to temperature.

The uncertainty of the influence of fluctuation is 0.001ppm. In order to determine the temperature coefficient of the foil resistance, we put them in the air tank, set the relative humidity to 44%, and change the temperature according to the gradient (28°C 24°C 23°C 22° C 18°C 22°C ) for 2 cycles of testing. Measure the resistance of 12 resistor respectively, and calculate the temperature coefficients of the first and second terms.

Result: The temperature drift of the resistor with the worst temperature coefficient (labeled L) in the measurement results is about 0.15ppm/°C, while the other temperature drifts are all within 0.1ppm/°C. Using the statement in the previous paragraph, the resistance will be blocked when the temperature fluctuates 0.01℃.

The uncertainty due to temperature fluctuations in the value measurement is 0.001 ppm. It can be seen that the foil resistance material has excellent temperature drift characteristics.

2. Long-term stability

Some experimental results show that the resistance has undergone huge changes in humidity, temperature and atmospheric pressure and the influence of environmental factors on the resistance has been tested. The resistance change after 365 days is still less than 0.1ppm, and the 12 resistances are all in Within the range of ±0.1ppm, it indicates that the drift rate of the resistor is lower than 0.1(ppm)/year. During the observation period, 

some curves occasionally fluctuate beyond the range of ±0.1ppm, but eventually return to the range. You can see the technology The technical standard resistance is extremely excellent long-term stability.

In the actual selection process, many engineers or purchasers have some deviations in the understanding of standard resistance and ordinary precision resistance. Next, let's talk about the difference between standard resistance and ordinary precision resistance.

1. Application differentiation

Generally, high-precision signal conversion, bridge circuits, sampling circuits, precision voltage dividers, etc. are commonly used in ordinary precision resistor, while standard resistor are usually used in the laboratory's inherent resistance reference, reference transfer and calibration.

2. Parameter distinction

The temperature coefficient of ordinary precision resistor mainly considers the resistance drift caused by environmental temperature changes and resistance and circuit heating. The unit is mostly a temperature coefficient of ppm/°C. Standard resistor are mostly used in the constant temperature environment of the laboratory.However, the temperature coefficient is still very demanding, and it is necessary to accurately give the first-order temperature coefficient ppm/°C and the second-order temperature coefficient ppm/°C2. The stability of ordinary precision resistor is mainly aimed at the stability of load life, the parameters say It is generally stated that the resistance drift under a load of several thousand hours. The unit is mostly a percentage, and the standard resistance does not need to be under load all the time. The stability is the annual stability, and the unit is ppm/year.

Accuracy: Standard resistor are used as reference standards, and their accuracy is more than one ten thousandths, ordinary precision resistor are generally up to one ten thousandths. A stable set of standard resistor is not only used in the maintenance and calibration of resistance standards. It plays an important role, and the high standards required for parameters are not achievable by ordinary precision resistor.