Micro Motion RFT9709 Instrukcja Obsługi Pobierz pdf (Strona 150)

136

Using ProLink

Software with Micro Motion

Transmitters

Calibrate Menu

continued

Programming auto zero for RFT9739

Diagnosing zeroing failure

If zeroing fails, indicators in the Status window switch ON. To view the

Status window, open the View menu, then choose Transmitter Status.

• The Calibration Failure indicator switches ON

• If the transmitter is an RFT9739, RFT9712, or RFT9729, the Zero

Too Noisy, Zero Too High, or Zero Too Low might also switch ON.

The most common sources of zeroing failure are:

• Flow of fluid through sensor during zeroing

• Partially empty sensor flow tubes

• An improperly mounted sensor

To clear a zeroing error, re-zero the transmitter after correcting the

problem, or cycle power to the transmitter to abort the procedure and

return to the previously established zero. For an RFT9739, adjust the

programmable auto zero parameters before re-zeroing. See

Section 14.3

14.3 Programming auto zero for

RFT9739

If Calibration Failure switches ON in the Status window, auto zero has

failed. If the Zero Too Noisy, Zero Too Low, or Zero Too High indicator is

also ON, and the zeroing procedure was performed on an RFT9739, the

auto zero parameters can be reprogrammed.

During the zeroing process, the RFT9739 measures the time shift (the

time between signals from the left and right sensor pickoff coils) for each

measurement cycle, computes the average time shift per cycle, then

derives the standard deviation of the average time shift over the zero

time.

• If zeroing is too noisy, the user can program a standard deviation limit

to account for mechanical noise from vibrating pumps or other

equipment. Mechanical noise can cause zero failure by interfering

with signals from the sensor.

• Zero time is the number of measurement cycles required for

transmitter zeroing, where one measurement cycle equals two tube

periods. The default zero time is 2048 cycles (approximately 40

seconds at a tube frequency of 100 Hz). A longer zero time might

improve the accuracy of the zeroing procedure by increasing the

number of measurement cycles.

Convergence limit

To reprogram the convergence (standard deviation) limit, enter the

desired value into the Convergence Limit text box (see

Figure 14-1

page 135). Record the convergence limit in the appropriate Flowmeter

Calibration Record in

Appendix F

, page 189.

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