The BMEAHI0812 eX80 HART analog input module supports 4-20 mA analog communication and HART digital communication on each of 8 input channels. The module operates with voltage inputs and includes 8 read resistors connected to the terminal block to convert current inputs.
The eX80 HART analog input module is powered by the backplane.
NOTE: The backplane does not provide power to the 4-20 mA current loop or to any sensor, transmitter, or other device connected to the current loop. You need to provide a source of 24 Vdc power to the current loop, as described in the wiring topic.
The BMEAHI0812 eX80 HART analog input module measurement refresh rate is 4 ms. This refresh rate remains constant, no matter how many channels are enabled (or disabled).
NOTE: The module measurement refresh task is not synchronized with the PLC scan. Therefore, you need to include the PLC scan time when estimating an overall application refresh rate.
Overflow/Underflow Control
Each input on the BMEAHI0812 eX80 HART analog input module operates over a range of 4-20 mA. You can use Control Expert to
map up to 5 current ranges for each input.
Upper and lower tolerance detections are enabled regardless of overflow/underflow control.
Depending on the range specified, the module checks for overflow and verifies that the measurement falls between a lower and an upper threshold:
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Designation
|
Description
|
|
Nominal range
|
The specified measurement range
|
|
Upper tolerance area
|
The range of values between the maximum value for the nominal range (20 mA) and the upper threshold
|
|
Lower tolerance area
|
The range of values between the minimum value for the nominal range (4 mA) and the lower threshold
|
|
Overflow area
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The range of values located above the upper threshold
|
|
Underflow area
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The range of values located below the lower threshold
|
NOTE: Monitoring of values in the overflow and underflow area can be enabled or disabled in Control Expert. Monitoring of the lower and upper tolerance areas is enabled and cannot be disabled.
The values of the thresholds are configurable independently from one another. Both the default values, and the maximum and minimum configurable values are as follows:
|
Range
|
BMEAHI0812 Range
|
|
Underflow Area
|
Lower Tolerance Area
|
Nominal Range
|
Upper Tolerance Area
|
Overflow Area
|
|
Default setting
|
–2,400
|
–801
|
–800
|
–1
|
0
|
10,000
|
10,001
|
10,800
|
10,801
|
16,200
|
|
Minimum / Maximum
|
–32,768
|
...
|
...
|
...
|
...
|
...
|
...
|
...
|
...
|
32,767
|
Measurements may be displayed using the standard format (in %, to 2 decimal places):
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Type of Range
|
Display
|
|
4-20 mA
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from 0 to 10,000 (0% to 100%)
|
It is also possible to define the range of values within which measurements are expressed, by selecting:
The lower and upper thresholds can be integers between –32,768 and +32,767.
For example, imagine a conditioner providing pressure data on a 4-20 mA loop, with 4 mA corresponding to 3,200 millibar and 20 mA corresponding to 9,600 millibar. You have the option of choosing the format, by setting the following lower and upper thresholds:
-
3,200 for 3,200 millibar as the lower threshold
-
9,600 for 9,600 millibar as the upper threshold
In this case, values transmitted to the program vary between 3,200 (= 4 mA) and 9,600 (= 20 mA).
When the HART function is enabled for the channel, the HART signal is filtered by the low pass filter in the BMEAHI0812 eX80 HART analog input module before being read by the analog input. The 3 dB cut-off frequency is about 10.0 Hz.
The type of filtering performed by the system is called first order filtering. The filtering coefficient can be modified from a programming console or via the program.
The mathematical formula used is as follows:
α = efficiency of the filter
Measf(n) = measurement filtered at moment n
Measf(n-1) = measurement filtered at moment n-1
Valb(n) = gross value at moment n
You may configure the filtering value from 7 possibilities (from 0 to 6). This value may be changed even when the application is in RUN mode.
The filtering values depend on the T configuration cycle (where T = module refresh time):
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Desired Efficiency
|
Required Value
|
Corresponding α
|
Filter Response Time at 63%
|
Cut-Off Frequency (in Hz)
|
|
No filtering
|
0
|
0
|
0
|
0
|
|
Low filtering
|
1
2
|
0.750
0.875
|
4 x T
8 x T
|
0.040 / T
0.020 / T
|
|
Medium filtering
|
3
4
|
0.937
0.969
|
16 x T
32 x T
|
0.010 / T
0.005 / T
|
|
High filtering
|
5
6
|
0.984
0.992
|
64 x T
128 x T
|
0.0025 / T
0.0012 / T
|
NOTE: When HART communication is enabled, operation of both the HART filter and the digital filter may cause excessive latency.
The process of alignment involves the elimination of an observed systematic offset, around a specific operating point, for a given sensor. Sensor alignment compensates for a detected variation that is linked to the process. Replacing a module does not require a new alignment. However, replacing the sensor or changing the sensor operating point requires a new alignment.
Conversion lines are as follows:
The alignment value is editable from a programming console, even if the program is in RUN mode. For each input channel, you can:
The alignment offset may also be modified through programming.
Channel alignment is performed on the channel in standard operating mode, without any effect on the channel operating modes.
The maximum offset between measured value and desired (aligned) value may not exceed +/-1,500.
NOTE: To align multiple analog channels on the BMEAHI0812 eX80 HART analog input module, proceed channel by channel, aligning one channel at a time. Test each channel after aligning it before proceeding to align the next channel.
