Instrument question

This type of question is actually very simple; there’s no need to overthink it – just choose the longest one among the three short ones! :Lol, actually, some transmitters allow setting at -70, while others require -69 or a higher value in order to set the zero point. However, even if it’s possible to set it that way, the accuracy isn’t guaranteed. When selecting the range for a pressure transmitter, it’s similar to choosing a range for a weight sensor – you can’t use a device designed to measure 1 kilogram to measure pressure of 1 kilogram! One must have principles in life, and the same goes for making watches!

. Instrument zero shift is the process of moving the measurement lower limit of the instrument to a certain position； For transmitters with a measurement range of 10~60 kPa, the lower measurement limit is 10 kPa ； The migration range of ±60 kPa refers to the allowable adjustment of the lower measurement limit within the range of -50 to +70 kPa through migration, while keeping the range unchanged ； For the QBC/DBC series of transmitters, changes in the range affect the range of permissible drift. That is: the actual allowable drift = |Basic drift + (Basic range – Actual range)| = |60 + (50 – 40)| = ±70 (kPa). Here, the basic drift and basic range refer to those values given in the instrument’s technical manual; these are assumed to be the same as the values stated in the question. In this case, the measurable lower limit (i.e., the range of drift) is from -60 to +80 kPa. It can be seen that the value D mentioned in the question falls outside the range for which drift is possible for this instrument. The last time I did a problem like this was almost 50 years ago:lol :lol

I have a question: Changing the range affects the range of the migration amount. What is the principle behind this, and how was this calculation formula derived?

The transmitter mentioned in the question is a QBC transmitter. This type of transmitter operates by measuring forces such as applied force, feedback force, and migration force, which all act on a lever to achieve equilibrium. The factor that determines this equilibrium state can be attributed to the displacement allowed by the measuring element (diaphragm box). When the allowable displacement of the diaphragm box remains at its limit, any change in one of these forces requires corresponding changes in the other forces in order to keep the diaphragm box at that limit position. There are only a few sources that use that formula to illustrate interrelationships, and it differs considerably from the actual situation; avoid using it if you don’t want to get stuck in complicated considerations.

Niubijia Lou is highly knowledgeable and extremely well-versed in many fields