Allen-Bradley Compact 1769-IR6, Руководство пользователя

Страница: 55 / 116

Publication 1769-UM005A-EN-P
Module Data, Status, and Channel Configuration 4-15
change from Program-to-Run or if any online configuration change is
made to a channel.
Selecting Excitation Current (Bit 3)
The module is capable of exciting each individual RTD/resistance device
with either 0.5 mA or 1.0 mA of current. Setting bit 3 to 0 provides 1.0 mA,
while a setting of 1 provides 0.5 mA.
The 0.5 mA excitation current is recommended for use with 1000
Ω
RTDs
and 3000
Ω
direct resistance inputs. An excitation current of 1.0 mA is
recommended for all other RTDs except the 1000
Ω
devices, and all other
direct resistance devices except the 3000
Ω
devices. Refer to the input
device literature for the manufacturer’s recommendations.
Setting Filter Frequency (Bits 0 to 2)
The module supports filter selections corresponding to filter frequencies
of 10 Hz, 50 Hz, 60 Hz, 250 Hz, 500 Hz, and 1 kHz. Your filter frequency
selection is determined by the desired range for the input type, and the
required effective resolution, which indicates the number of bits in the
channel configuration word that do not vary due to noise. Also consider
the required module update time when choosing a filter frequency. For
example, the 10 Hz filter provides the greatest attenuation of 50 and 60 Hz
noise and the greatest resolution, but also provides the slowest response
speed.
The choice that you make for filter frequency will affect:
•
noise rejection characteristics for module input
•
channel step response
•
channel cutoff frequency
•
module autocalibration
•
effective resolution
•
module update time
NOTE
A lower excitation current reduces error due to RTD
self-heating, but provides a lower signal-to-noise ratio.
See the manufacturer’s recommendations for your
particular RTD.
AB PLCs