User Manual

Compact IO™ Isolated HART Analog Input Module
U ser 's M a n u a l 0 300 21 5- 03 R ev. A
6-8
Table 6-4 (Filter Frequency and General Settings)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
60 H z
0
0
0
0
50 Hz
0
0
0
1
28.5 Hz
0
0
1
0
300 Hz
0
0
1
1
360 Hz 0100
Disable
0
Enable
1
Disable
0
Enable
1
Disable
0
Enable
1
Disable
0
Enable
1
Disable
0
Enable
1
Disable
0
Enable
1
Disable
0
Enable 1
Reserved
Set To Zero 0000
Disable
0
Enable
1
EI (E nable Interrupt)
AL (A la rm La tc h )
EA (Enable Al arm)
To Select
M ake the se bit se ttings
EC (Enable Chan nel)
S lot Code 0
S lot Code 1
S lot Code 2
S lot Code 3
Filt er Frequenc y
Input Filter Selectio n ( Bits 0 through 3)
Each channel can be configured for five different filter setti ngs. Select one of the five
filters, for the associated channel.
Effects of Filter Frequency on Noise Rejection
The filter frequency that you choose for a module channel determines the amount of
noise rejection for the inputs. A lower frequency (50 Hz versus 300 Hz) provides better
noise rejection and increases e ffective resolutio n, but also increases channel update time.
A higher filter frequency provides lower noise rej ectio n, b ut decr eases the channel update
time and effective resolution.
When selecting a filter frequency, be sure to co nsider cut-off frequency and channel step
response to obtain acceptable noise rejection. Choose a filter frequency so that your
fastest-changing signal is below that of the filter’s cut-off freq uenc y.
Common Mode Rejection is better than 60 dB at 50 and 60 Hz, with the 50 and 60 Hz
filters selected, respectively, o r with the 28.5Hz filter selected. The module performs well
in the presence of common mode noise as long as the signals ap plied to the user positive
and negative input terminals do not exceed the common mo de voltage rating (±500V) of
the module. Improper earth ground may be a source of common mode noise.
NOTE: Transducer power supply noise, transducer circuit noise, or process variable
irregularities may also be sources of no rma l mo de noise.
Effects of F ilter Frequency on Channel St ep Response
The selected channel filter frequency determines the channel’s step response. The step
response is the time required for the analog input signal to reach 100% of its expected
final value, given a full-scale step change in the input signal. This means that if an input
signal changes faster than the channel step response, a portion of that signal will be
attenuated by the channel filter. T he channel step resp o nse is calculated b y a settling ti me
of 3 x (1/filter frequency).
!
Attention
The R eal Time Sample rat e must b e greater than or equal to the slowest
channel step response time or a configura t ion error will occur.