Micro Motion RFT9709 Manuál s instrukcemi stáhnout pdf (Strana 151)

Using ProLink

Software with Micro Motion

Transmitters

137

Calibrate Menu

continued

Programming auto zero for RFT9739

Applications Menu Help Menu

Configure Menu:

Meter Factors

Calibrate Menu Test Menu

Programming the limit of the standard deviation causes the RFT9739 to

zero in one of the following ways:

• When the standard deviation measured by the transmitter converges

to a value that is less than the programmed standard deviation limit,

the RFT9739 will successfully zero. The time required for zeroing to

be completed will be equal to or less than the configured zero time.

• If the standard deviation measured by the transmitter exceeds, but is

not more than 10 times the programmed standard deviation limit, the

RFT9739 will successfully zero, but will continue sampling

throughout the entire zero time.

• If the standard deviation measured by the transmitter is more than 10

times the programmed standard deviation limit, the RFT9739

indicates zero failure and retains the previous zero calibration. This

condition indicates a fault.

Zero time

The user can program a zero time of 100 to 65,535 cycles. 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.

To program the zero time for the RFT9739, enter the desired number of

measurement cycles into the Zero Time text box (see

Figure 14-1

page 135). Record the zero time in the appropriate Flowmeter

Calibration Record in

Appendix F

, page 189.

Example:

Given:

The default zero time is 2048 measurement cycles,

approximately 40 seconds at a tube frequency of 100 Hz. Under zero

flow conditions, the sensor flow tubes vibrate at a rate of 100 Hz, or 50

cycles per second.

Problem:

Because the process does not allow flow to be stopped for

the amount of time usually required for auto zeroing, the RFT9739

needs to zero in 10 or fewer seconds.

Solution:

Since 10 seconds ⋅ 50 measurement cycles/second = 500

cycles, the zero time is 500.

Enter a value of 500 into the Zero Time text box. The transmitter will

zero in 10 or fewer seconds, unless the measured standard deviation

is 10 times the programmed convergence limit during the auto zero (in

which case, the RFT9739 will indicate zero failure).

If the RFT9739 cannot zero because the programmed limit of the

standard deviation is too small, enter a larger value into the

Convergence Limit text box.

1 2 ... 146 147 148 149 150 151 152 153 154 155 156 ... 213 214

Komentáře k této Příručce

Žádné komentáře

Micro Motion RFT9709 Manuál s instrukcemi Strana 151

Komentáře k této Příručce