Toshiba LF494 - Manual (Page 83)

TOSHIBA
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8.2.14 Kate-Of-Change Limit
The ratc-of-changc limit is used lo diminaie high ekclrical noise contained in the process
flow signal.
To check electrical noise, two parameters are defined: rate-of-uhange limit (set in percent
value of the span) and control limit :ime (set in units of seconds). Normally the flowmeter
produces the analog output signal by sampling the How rate signal at 1/24 (or 1/12) of a
second sampling rate, H the sampled value exceeds the set rate-ol-changc limit value based
on the averaged flow rale value up vniil the sampled time, the system will reject that
sampled value and instead the averaged value including the raie-of*change limit value in
place of the rejected sampled value will be output. However, if the limlr-cxceeding sampled
value continues for the same flow direction for more than the preset control limit time, that
diïta will be used as the output signal. The setting ranges for these two parameters are as
follows;
• Rate-of-change limit
0 lo 20 %/sampling rate (in incremenis of 0,5 %)
Where the sampling rate is either ly'24, 1/12 or 1/6 of a second depending on the
excitation frequency as shown below:
Excitât ion freq ucncy Samplingrate
24
11/.
1/24 sec
12 Hz or
6
Hz L/12 sec
• Control limit timet 0 to 20 sec {in increments of 1 second)
NOTE
If
“iT
is set in cither of these parameters, the rate-of-changc limit function is disabled.
Proceed as follov-'s to cheek or change the ralc-of-change limit value and the control limit
time.
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