Regarding the issue of transmitter migration amount
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Question: When calibrating a transmitter to zero, does it mean adding or subtracting the same value from both the lower and upper limits of the transmitter’s range??? Thank you for asking.
Hehe, you're right. That’s simply how it is. The range does not change, so add and subtract the same amount. Migration is divided into positive migration and negative migration; positive migration results in an increase, while negative migration results in a decrease.
It can be understood this way, but in practice, only the zero point needs to be adjusted.
What you are saying is incorrect. Both zero shift and zero adjustment of the transmitter are used to set the output at zero (4 mA DC), but they serve different purposes; therefore, they are not the same thing. The zero adjustment of the transmitter is the adjustment of the zero point when the input pressure or differential pressure is 0, but the output is not 0 ； The zero-point offset adjustment of the transmitter is the adjustment that sets the output to 0 when the input pressure or differential pressure is not at 0.
Isn’t that what the book says? The amount of migration only changes the zero point of the range, while the range itself remains unchanged.
I support the opinion from the fourth floor. The zero-point migration and adjustment of transmitters are not the same thing. Zero-point adjustment involves using a 4MA zero-point calibration signal as input; it is not a adjustment for when the actual output is not 4MA. Zero-point migration, on the other hand, is relative to the site conditions – if the transmitter is installed at a location that is not the actual zero-point position in the process, then migration is necessary. The specific amount of migration is determined by subtracting the pressure in the negative-pressure chamber from that in the positive-pressure chamber
Take a hydrostatic level gauge, for example: if the lower limit of its measurement range is positive, it undergoes positive migration; if it is negative, it undergoes negative migration.
The migration volume is obtained by subtracting the negative pressure from the positive pressure; it also depends on the density of the medium