Specifications - ACR Electronics SmartReader Plus Reference Manual

impedance. This simply refers to how much resistance your instrumentation (for example, the
SmartReader Plus 7) can have before it will begin to cause problems. For voltage inputs, a
very high impedance is usually required (greater than 10k ohms). This prevents the
unnecessary draining of current from the transducer circuit. The SmartReader Plus 7's
voltage inputs are all high impedance (greater than 1M ohms).
For current loop inputs, it is advantageous to have a very low impedance (the SmartReader
Plus 7's current channels have a low 20 ohm impedance). This helps to minimize the voltage
requirements and power consumption of the circuit. Check the specifications for the
transducers you intend to use to ensure the SmartReader Plus 7's input impedance is
acceptable.
Two-Wire Transmitters
Two-wire transmitters are transducers that form part of a current loop circuit. They vary the
current flow in accordance with changes in the variable which they are sensing. Most two-wire
transmitters have a 4-20mA output.
Three-Wire Transducers
Three-wire transducers have three connections: a supply (excitation) voltage input (V+IN), an
output voltage (V+OUT) and a common (COM-). You can usually tell if a transducer is 3-wire
by reviewing the wiring diagram and looking for a single common connection.
Four-Wire Transducers
Four-wire transducers fall into two categories: line-type and Wheatstone bridge types. No
more than one line-type transducer can be attached to a SmartReader Plus 7 unless it has an
isolated output (no electrical connection to the line). More than one bridge-type transducer
can only be hooked to a SmartReader Plus 7 if each has an isolated power supply.
Output
The specified output of a transducer or transmitter will determine whether it is compatible for
use with your SmartReader Plus 7. Some of the most popular transducer outputs (such as 0
to 2.5V or 0 to 5V DC) are directly compatible with the logger. The most popular transmitter
output is 4 to 20mA which can easily be used with the SmartReader Plus 7.
1.10.6

Specifications

Voltage and Current Inputs
Ranges:
Resolution:
Accuracy:
Input Impedance:
Copyright © 2010 ACR Systems Inc. All Rights Reserved.
SmartReader Plus Data Logger
0 to 2.5 volts DC
0 to 5 volts DC
0 to 10 volts DC
0 to 200mV DC
0 to 25mA
0.025% (12-bit)
±0.5% full scale
>1 megohm (all voltage channels)
20 ohms (0 to 25mA channels)
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