Toshiba LF434 - Manual (Page 85)

TOSHIBA
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S 2 A 4 Rate*Of-Change Limit
The riite-of-changc limit is used to eliminate high dectricftl noise contained in the process
flow i^ignal.
To check electrical noise, two parameters arc defined: rate-of-change limit (set in percent
value of the span) and control limit rime (set in units of seconds). Normally ihe flowmeter
produces the analog output signal by sampling the flow rale signal at 1/24 (or 1/12) of a
second sampling rate. If the sampled value exceeds the set rate-of-ehange limit value based
on the averaged flow rate value up until Ihc sampled lime, the system will reject that
sampled value and instead the averaged value including Ihe ratc-of-changc limit value in
place of the rejected sampled value will be output. However, if the limit-exceeding sampled
value cominues for the same flow direction for more than the preset control limit lime, that
data will be used as the oulpul signal The setting ranges for these two parameters are as
follows:
* Rate-of-chtmge limit
0 to 30 %/sampling rale (in increments of 0.3 %)
Where the sampling rate is either 1/24,1/12 or 1/6 of a second depending on the
excitation frequency as shown below:
Excitation frequency Sampling rale
24 Hz 1/24 sec
12IIzor6Hz 1/12 sec
- Control limit time: Ü to 20 sec (in increments of 1 second)
NOTE
If ‘*0’’ is sel in either of these parameters, the rate-of-change limit function is disabled.
Proceed as follows to check or change the raie-of-change limit value and the control limit
lime.
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