How to resolve discrepancies between on-site instruments and secondary instruments
Thread Content
How to resolve discrepancies between the cumulative values of field instruments and secondary instruments. The field instrument is an electromagnetic flowmeter, while the secondary instrument is an intelligent flow totalizer with temperature and pressure compensation.
Is the signal received by the integrator the signal from the electromagnetic flowmeter? There shouldn’t be a need for temperature and pressure compensation, right? ； Generally, the readings at the field site and those on the secondary meters do not match. If there is no issue with the wiring, it is necessary to check whether the small-signal cutoff settings of the two meters are identical.
The signals received by the integrator can be analog signals, which results in lower precision and greater deviations. The precision of receiving pulse signals is high, with minimal or even no deviation. Electromagnetic flowmeters have an accumulation function built into them; why not simply use the accumulated value from the electromagnetic flowmeter? If it is due to an upload issue, HART communication or other intelligent communications can solve it.
The integrator receives an analog signal of 4–20 MA. The on-site instruments are installed at a relatively high position, making it difficult to view them. Therefore, the signal is sent to the intelligent flow integrator in the control room, where it is accumulated by the integrator. How can the cumulative errors of an electromagnetic flowmeter and that of an accumulator be kept low? The settings for filtering out weak signals in both instruments should be the same
It’s probably a setting issue; a small resection is needed~·
Firstly, secondary instruments do not support temperature and pressure compensation. Secondly, compare the cumulative values of the two flow rates under normal operating conditions; select cumulative values from several different time periods to see if there is any constant factor at play, as this could be the cause of the difference between the two values. This is achieved by modifying the secondary instrument or by multiplying its cumulative value by a correction factor.
Analog signals in the 4–20 MA range will have errors; they can only be used for flow display. To avoid errors, cumulative values must be counted using pulse signals! That’s how our factory uses it on the DCS!
It is normal to have errors; the data from the on-site flow meter should be taken as the reference
It’s practically impossible to maintain a 4-20MA signal constantly, as it’s too susceptible to interference. It’s recommended to use frequency; even better, volume equivalent can be used, with almost no error
I agree with what was said on the seventh floor: analog signals cannot have their cumulative amount measured. Pulse quantity should be used.
It’s normal to have errors; removing the temperature and pressure compensation from the integrator should fix it