Choosing Input Channels - ACR Electronics SmartReader Plus Reference Manual

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Avoiding Ground Loops

Take special care to avoid ground loop problems when you use your SmartReader Plus 7. A

ground loop can occur when there is more than one path to ground in your logger-transducer

circuit. Ground loops can damage your SmartReader Plus 7 as well as your transducers. To

avoid ground loop problems in your SmartReader Plus 7 circuit:

Do not use more than one grounded power supply to excite your transducers.

Do not connect your logger to your computer for Realtime readings unless:

· your computer is battery-operated (i.e. not grounded) or

· your transducer power supply is not grounded.

If you must use more than one grounded power supply in your SmartReader Plus 7 circuit,

each transducer you use must be isolated. If you must use non-isolated transducers, then you

must use a Signal Repeater/Loop Isolator between the transducer output and the

SmartReader Plus 7 input.

Wiring Notes and Considerations

The SmartReader Plus 7 has four common inputs (labeled "Common"). These are not

isolated from each other and can be used as the negative "-" connection for the power

supply (or battery) and any of the transducers being logged by the SmartReader Plus 7.

The 200mV channels "float" when no connection is made to them. They can be expected

to read a positive voltage when left unconnected. When connected, however, they will

read the correct input voltage.

The 25mA channels read positive current only. Make sure to observe polarity. If you are

using both channels simultaneously, ensure that both 4-20mA transmitters operate with

their negative (-) terminals tied together.

1.10.3

Choosing Input Channels

The SmartReader Plus 7 has seven external input channels to use in your particular

applications.

The resolution of your SmartReader Plus 7 logger is twelve bits. This means that it can

resolve analog signals into 4096 discrete steps. All channels have a resolution of 0.025% full

scale (1/4096 x 100%) which produces a very detailed graph in most applications.

The SmartReader Plus 7 can be used for measuring signals with a full scale output as low as

20mV on the 200mV channel (this translates to 1 part in 410 which is better than eight bit

resolution); this is useful for Wheatstone bridge type transducers which typically have a full

scale output in the tens of millivolts.

WARNING: The 200mV channel is more sensitive to noise signals generated by

the environment the logger is placed into - shielded cables should be used.

SmartReader Plus Data Logger

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