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C-002RX32.7680K-E:PBFREE Datasheet(PDF) 6 Page - Texas Instruments
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Connecting Other Signal Sources
In general, the ADS1x31REF can accurately measure any voltage in the input range of the installed ADS
device, as long as the following rules are observed:
Never apply a negative voltage to the inputs of the ADS1x31REF. The installed ADS device cannot
accept negative voltages at its input. Applying negative voltages may damage both the device and the
ADS1x31REF. (The negative signs used in some signal names indicate inversion, not polarity.)
For single-ended signals, ground the negative input or connect it to 2.5V. 2.5V is available from a
voltage divider by shorting J7; see Section 6.4.5 for details.
The input range of the amplifier on the ADS1131 or ADS1231 does not extend to the supplies. See the
ADS1131 data sheet or the ADS1231 data sheet for details.
Note that Scale mode is designed only for use with load cells. Although it can be tested with a voltage
source or resistive divider, Scale mode does not, in general, display meaningful data unless a load cell is
connected and calibration is performed.
Connecting an External Clock
Note that only the ADS1231 can receive an external clock. To connect an external clock, connect a clock
oscillator to the EXTCLK test point. No settings need to be changed; the ADS1231 will automatically use
the attached clock.
The clock source must conform to 3.3V TTL or CMOS logic rules.
Shorted-Input Noise Test
The noise measurements given in the product data sheet are taken with the inputs shorted to 2.5V. These
noise measurements can be replicated on the ADS1x31REF with no external hardware. To set up these
measurements on the ADS1x31REF, perform the following steps:
1. Move the mode switch to Analysis mode.
2. Short jumpers J8 and J7. (These jumpers are located very near the terminal block, and are marked
Input Shorting Jumpers in Figure 1.)
3. Set up the installed ADS device as desired, as described in the previous sections.
4. Hold down the DISP button. The display shows the current display mode. While holding down DISP,
press the MODE button until the word on the left side is
5. While still holding down DISP, press the UNIT button until the word on the right side is
6. Release the DISP button. The display shows the word
followed by an increasing number. Once
the appropriate number of points is collected, the calculated noise voltage is displayed. This value is
the shorted-input RMS noise voltage, input-referred.
The first RMS noise measurement may be incorrect as a result of device settling. The second
measurement is generally correct.
For a detailed description of Analysis mode, see Section 3.
The following items are required to measure mass with the ADS1x31REF:
A load cell, connected as described in Section 1.4
An object of known mass within the load cell range
To avoid performing calibration on each power-up, you can save the calibration settings to flash memory.
See Section 3.4.1 for details.
ADS1131REF and ADS1231REF
– July 2010 – Revised August 2011
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