Measurement Computing Personal Daq rev.6.0 - Manual (Page 24)

2-4 General Information & Specifications 878595 Personal Daq User’s Manual
Optical Isolation
The Personal Daq is optically isolated from its host PC by up to 500 VDC. This means that an inadvertent
application of such voltage to Personal Daq will not affect the PC. In addition to optical isolation, Personal
Daq maintains all sensitive acquisition-related circuitry external to the PC. This physical isolation of
circuitry from the PC results in less noise and more accurate measurements.
A/D Conversion
Personal Daq uses a sigma-delta analog/digital converter to provide high resolution and sensitivity. When
scanning multiple input channels, resolution and speed can be selected from 22 bits at 1.6 samples/sec, to
15 bits at 80 samples/sec (not including cold-junction compensation).
You can select resolution and speed on a per-channel basis, allowing you to match parameters to individual
channel requirements. For example, you could select 21 bit resolution to detect small temperature changes
on one channel, and select 15 bit resolution to measure battery voltage on a second channel. Although
each channel can have a different resolution and measurement period, all channels are scanned at the same
rate to ensure sampling interval integrity. Examples of scan sequences, with various channel resolutions
and calibration arrangements, appear in the figure on page 2-7.
Input Ranges
You can individually select the input range for each channel. For example, one channel could be used for
volts and another for temperature. Personal DaqView automatically assigns the appropriate units
depending on two factors:
• the selected range and
• measurement unit preferences
Measurement unit preferences can be modified from Personal DaqView’s Preferences Dialog Box located
in the View pull-down menu of the Main Control Window. Chapter 4 provides more detailed information.
Note: The maximum voltage input range (full scale) is –10 to +20 VDC. The lowest programmable
voltage input range is -31 to +31 mV. A complete list of Personal Daq’s programmable ranges
appears on page 2-8.
Each analog input channel has the following user-specified measurement parameters:
• signal type: volts, or thermocouple type J, K, T, E, R, S, B, or N
• full scale voltage: from -10 to + 20 VDC; with programmable ranges as indicated on page 2-8.
• resolution/sample period: from 22 bit RMS at 1.6 samples/sec, to 15 bit RMS at 80 samples/sec
(note that these rates were obtained with a 10-channel scan, continuous self-calibration disabled,
and are for measurements with no CJC [cold junction compensation])