National Instruments FP-Al-110 用户手册

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页码 20
FP-AI-110 and cFP-AI-110
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Overranging
The [c]FP-AI-110 has an overranging feature that measures a little 
beyond the nominal values of each range. For example, the actual 
measurement limit of the 
±10 V range is ±10.4 V. The overranging 
feature enables the [c]FP-AI-110 to compensate for field devices 
with span errors of up to +4% of full scale. Also, with the 
overranging feature, a noisy signal near full scale does not create 
rectification errors.
Filter Settings
Three filter settings are available for each channel. The filters on 
the [c]FP-AI-110 input channels are comb filters that provide 
notches of rejection at multiples, or harmonics, of a fundamental 
frequency. You can select a fundamental frequency of 50, 60, or 
500 Hz. The [c]FP-AI-110 applies 95 dB of rejection at the 
fundamental frequency and at least 60 dB of rejection at each of 
the harmonics. In many cases, most of the noise components of 
input signals are related to the local AC power line frequency, so 
a filter setting of either 50 or 60 Hz is best.
The filter setting determines the rate at which the [c]FP-AI-110 
samples the inputs. The [c]FP-AI-110 resamples all of the channels 
at the same rate. If you set all of the channels to the 50 or 60 Hz 
filter, the [c]FP-AI-110 samples each channel every 1.470 s or 
every 1.230 s, respectively. If you set all of the channels to 500 Hz 
filters, the module samples each channel every 0.173 s. When you 
select different filter settings for different channels, use the 
following formula to determine the sampling rate.
(number of channels with 50 Hz filter
×184 ms +
(number of channels with 60 Hz filter
×154 ms +
(number of channels with 500 Hz filter
× 21.6 ms =
Update Rate
If you are not using some of the [c]FP-AI-110 channels, set them 
to the 500 Hz filter setting to improve the response time of the 
module. For example, if one channel is set for a 60 Hz filter, and 
the other seven channels are set to 500 Hz, the module samples 
each channel every 0.3 s (four times faster than the case in which 
all eight channels are set to the 60 Hz setting).
The sampling rate does not affect the rate at which the network 
module reads the data. The [c]FP-AI-110 always has data available 
for the network module to read; the sampling rate is the rate at 
which this data is updated. Set up your application so that the