How to calculate the allowable error of temperature controller?

It seems that it is necessary to seriously study the calibration of intelligent temperature control instruments, so let me say:

1, the landlord said that the calibration method is correct;

2. As for accuracy, it depends on the accuracy index on your instrument nameplate, such as 0.5%F.S, which means that the error will not exceed 5 ‰ of full scale, and you need to calculate the specific value. For another example, the error of an instrument with a measuring range of 1000 degrees will not exceed 5 degrees. If it exceeds 5 degrees, it will be unqualified!

As for how to deal with unqualified products, different instruments have different correction methods, depending on what instrument you are. Check the instructions and then consult the manufacturer. To be sure, the debugging and calibration of smart meters are all operated through menus, and you don't need potentiometers.

The basic principles of verification are as follows:

AD samples the amplified input signal and converts it into corresponding digital code, such as 1000~4096. When checking, let the CPU remember that 1048 is zero and 4052 is full scale, OK. Later, the CPU will distinguish the input signal according to this code, but after a period of time, the front-end amplifier circuit appears long-term drift, 65438+. It needs recalibration. That is, let the CPU reconfirm zero and full codes.

In other words, it is necessary to input the signal simulating the real sensor and confirm it through the menu.

In addition, it should be noted that in the calibration process of thermocouple digital display instrument, there is a compensation problem of cold end temperature, and the treatment methods of this problem will be different for different manufacturers' instruments. Before calibrating DDZ-3 instrument, it was necessary to subtract the millivolt value corresponding to the cold end temperature from the input millivolt signal. For example, if the ambient temperature is 25 degrees, the corresponding millivolt value is 0.52 millivolts. Whether it is zero or full, the value should be checked according to the scale table, and this 0.52 millivolt should be subtracted and added to the digital display table.

Some intelligent digital display meters can first remove the cold end temperature compensation through the menu, and then directly add the mV value to the scale.

However, most manufacturers do not have an open calibration method, which may be to prevent users from entering the calibration menu by mistake without conditions (such as potentiometers and resistance boxes), resulting in data loss.

Therefore, the safest way is to suggest returning it to the manufacturer for adjustment.