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SmartReader Data Logger
41
Copyright © 2010 ACR Systems Inc. All Rights Reserved.
0 to 100 mA
N / A
25mA, 10V
In the above table, the Range column lists examples of input signals that you may wish to
monitor using your SmartReader 7. The Standard column lists the channel you would
normally choose to monitor that particular signal. The Alternative column lists other channels
that can be used to monitor the same input signals. In most cases, these channels will need
to be fitted with external resistors.
Non-Standard Ranges
You may want to use a special transducer or tie into an existing process signal loop that does
not match the SmartReader 7's standard input ranges. The following step-by-step procedure
will help you choose which channel is best:
1. Determine the maximum output signal (M) and the zero offset signal (Z) of the transmitter
or circuit you wish to tie into. For example, a transducer with a specified range of 1 to 6
volts DC will have a maximum output signal of 6 volts and a zero offset signal of 1 volt. A
4 to 20 milliamp transmitter will have a maximum output signal of 20 mA and a zero offset
signal of 4 mA.
2. Determine the transducer's full scale output (F). You can do this simply by subtracting Z
from M. The full scale output of the 1 to 6 volt transducer is thus 5 volts. The full scale
output of the 4-20mA transmitter is 16 mA.
3. Compare M with the channels available on the SmartReader 7 and choose a channel
with an input equal or greater to this value (if available). If no such channel exists, then
modify one to suit by referring to the Customizing Input Ranges section.
4. Determine if the resolution (R) of the channel you chose in Step #2 will be adequate. You
can determine this, in percent, by using the following equation:
R = C * 0.4 / F
Where:
C = the input range of the channel you chose to use (in units of either millivolts, volts
or milliamps).
F = the full scale output of your transducer (M - Z) measured in the same units as for
C.
R = the resolution expressed in a percentage (%) of full scale output.
For example, a 0.5 to 2.5 volt transducer connected to the 2.5V channel will be logged
with a resolution of 0.5%. A 4 to 20mA transducer hooked up to the 25mA channel will
log with a resolution of 0.6%.
Generally, it is good practice to keep resolution to within 1% for most applications.
However, you might accept far coarser resolution in some applications and, in others,
require far better. You will be able to determine your own requirements after you have
become familiar with the results you can expect with different arrangements. If your
requirements demand greater resolution than what you calculated, then you should set up
your inputs with resistors as described in the Customizing Input Ranges section in this
chapter.
5. To find out in what actual steps (S) your logger will collect data, first determine the input (I
) of your transducer or transmitter. You can do this by subtracting the lowest level input
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