We often encountered in the occasion of using differential pressure transmitter
Zero migration & throughout;
Such a * * terms, what is a zero migration, why the need for zero migration, how to correctly implement zero migration.
About the difference of differential pressure transmitter are presented in this paper how to solve the problem of zero migration, and how to carry out the relevant instrument calibration to you as a simple narrative.
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Check and how to zero: when the input under range limit, caused by certain amount of influence the change of the output value.
Current limit value is not zero value, also known as the starting point migration (
Migration into free migration, negative transfer and positive transfer.
To the instrument input signal (
Relative to the range as the abscissa to output signals relative to the scope as the ordinate, can draw the instrument input/output characteristic curve, set as a linear relationship.
Characteristic curve slope is the same translation is called the zero migration.
Application of differential pressure transmitter when measuring liquid level, if the differential pressure transmitter of positive and negative pressure chamber and container pressure points in the same horizontal plane, there is no need for migration.
But in practice, for the equipment installation location and easy to maintain and other considerations, and measuring instrument is not necessarily can take pressure points in the same horizontal plane;
And as measured medium, which is highly corrosive or heavy viscosity liquid, can not directly introduce the medium pressure meter, you must install the isolation tank, to transfer pressure signal with spacer, in case by measuring instrument by corrosion.
Then consider medium and spacer fluid column effect on the pressure meter reading.
How to check differential pressure transmitter: preparation;
Calibration of conventional differential pressure transmitter;
Intelligent differential pressure transducer calibration.
Preparation: we know that in the application of differential pressure transmitter is connected to guide pressure tube, usually, need to press guide tube joint apart and differential pressure transmitter, then connected to the pressure source for calibration.
Calibration for differential pressure transmitter, the first three valve group, the positive and negative valve closed, open the balance valve, then unscrew bleed, drain valve or cocks vent, and then with homemade sub instead of positive pressure chamber exhaust, drainage valve or cock;
The negative pressure chamber is keep unscrew, make it through the atmosphere.
Pressure source through a rubber tube connected to the homemade joint, close the balance valve, and check the seal gas path, then the ammeter (
, hand device connected to the transmitter output circuit, after electrify preheating start calibration.
Of conventional differential pressure transmitter calibration: first the damping to zero state, first to the zero point, and then filled with pressure adjustable full scale, make the output to 20 ma, zero and full range adjustment after normal, check the middle scale, to see if the error?
When it is necessary for fine-tuning.
And then migrated, linear and damping adjustment work.
Smart differential pressure transmitter calibration: using the conventional method for calibration of intelligent transducer is no good, because this is determined by the HART transmitter structure theory.
Because smart transducer in the input pressure source and produce 4 -
Between 20 ma current signal, in addition to the machinery, circuit, and microprocessor chip operation work of the input data.
Do a 4 - first
20 ma fine-tuning, the rectification of transmitter internal D/A converter, because it does not involve the sensing component, without external pressure signal source.
Do it again the fine-tuning, 4 -
20 ma, digital readout in conformity with the actual pressure signal, so you need to pressure signal source.
Do after reset range, 4 - through adjusting the analog output
20 ma in conformity with the additional pressure source, its role and zero (transmitter enclosure
, the tuning range (
The effect of switch is exactly the same.
Above say so many, but users will just remember such a key point, that is: don't make any case of differential pressure transmitter bellows unidirectional compression.
Because is the differential pressure transmitter bellows differential pressure value of the actual measurement is a tiny, and unidirectional compression, the pressure will greatly beyond the affordability of bellows, bellows damage.
The order is not important, just remember the bellows is not impacted by the pressure.
By using the zero: shut down any valve, balance valve, close the valve.
Powerstation, open any valve, balance valve, open the valve.
Except, of course, add the spacer liquid level measurement, except with condensed water, double chamber equalizer which are such as boiler.
So then you can do it correctly to achieve the differential pressure transducer calibration and commissioning work.
In this paper by embellish instrument technology co. , LTD. Arrange release.
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