Acromag DT236-0600, Руководство пользователя, Страница: 32 / 40

Model DT23x-0600 Dual Two-Wire DC I/V Input Transmitters
Acromag, Inc. Tel: 248-295-0880 - 32 -
http://www.acromag.com
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Input … continued
Analog to Digital Converter (A/D):
Each input channel uses a 24-bit,

-

A/D
converter with only the first 16-bits used. Its signal is normalized to a bipolar range
count of ±25000 to simplify I/O scaling (see Input Resolution below).
Sampling Rate (A/D): Input ADC samples at a variable rate with filter as follows:
A/D SAMPLING RATE (SAMPLES/SECOND) PER INPUT FILTER
NONE
LOW MED HIGH
214.65sps 53.6625sps 13.42sps 1.6775sps
Input Impedance: Each channel has two input circuit paths A & B that support
different ranges. Input impedance will vary with the input path divider as follows:
INPUT IMPEDANCE PER MODEL INPUT PATH DIVIDER
MODEL INPUT A INPUT B
DT236-0700 24.9Ω Current Shunt No Divider
1
, 15MΩ
DT237-0700 No Divider
1
, 15MΩ 86.6K/(998K+86.6K) , 1MΩ
DT238-0700 28K/(499K+28K) , 500KΩ 5.36K/(998K+5.36K) , 1MΩ
1
Note: Direct connection to A/D channel without a resistive divider.
Input Overvoltage Protection: Inputs include Bipolar Transient Voltage Suppressers
and diode clamping along with series resistance and capacitive filtering.
Input Filter: RC filtering plus digital filtering, optimized and fixed per input range and
filter selection within the

-

ADC. See also Normal Mode Noise Rejection and
Output Response Time.
Noise Rejection (Common Mode): Varies by model with filter selection between no
filtering and high filtering as follows (measured with a 100

input unbalance):
Typical Common Mode Noise Rejection
MODEL
NO FILTER HIGH FILTER
DT236 93dB 139dB
DT237 71dB 119dB
DT238 70dB 113dB
Noise Rejection (Normal Mode): Varies with input filter level and input path divider.
The minimum measured rejection of the DT236 model is given which does not divide
its inputs. The higher rejection of the DT237 & DT238 is estimated by adding
20*log[input_divider] (see Input Resolution for applicable dividers per input path).
Typical 60Hz Rejection for Input Path A & B per Input Filter Setting
MODEL
None (dB) Low (dB) Med
1
(dB) High
1
(dB)
DT236 A, B: 6 A, B: 25 > 80dB
1
> 80dB
1
DT237 est A: 7, B: 28 A: 25, B: 47 > 80dB
1
> 80dB
1
DT238 est A: 32, B: 51 A: 50, B: 70 > 80dB
1
> 80dB
1
1
Note: At medium and high filter settings, the heavily attenuated 60Hz signal cannot
be measured due to 4
th
order filtering by the input ADC which adds 80dB minimum
of rejection at frequencies between 47Hz and 61Hz.
Bandwidth: The frequency where the DT236 is attenuated 3dB for each input filter
level setting is shown below (DT237 & DT238 similar). See also Normal Mode Noise
Rejection and Output Response Time.
Bandwidth (-3dB) per Input Filter Setting
MODEL None (dB) Low (dB) Med (dB) High (dB)
DT236 16Hz 7Hz 1Hz 100mHz