EXC-

SNS-

SNS+

SIG+

SIG-

EXC+

OUT+

EXC-

OUT-

EXC+

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1.2 Controls

The main controls for the ADS1x31REF are the four buttons and the mode selection slide-switch (see

Figure 1).

The slide-switch selects between weigh-scale (Scale) and Analysis modes. The ADS1x31REF switches

modes only when it is displaying data. If the switch is changed in a configuration mode, nothing happens

until the configuration mode is exited. At that time the ADS1x31REF reads the switch and enters the

selected mode.

The four buttons have different functions, depending on the operating mode. In Scale mode, the switches

have the functions in the box labeled SCALE. In Analysis mode, the switches have the functions shown in

the box labeled ANALYSIS. In configuration mode, the switches have the functions shown in the box

labeled CONFIG.

The buttons also have different names in different modes. In this document, they are identifed by the

respective names they have in the mode under discussion.

1.2.1 Auxiliary Controls

The Reset switch resets the board, except for the USB interface.

The USB Reset switch resets the USB interface. If USB communication fails, pressing USB Reset may

solve the problem.

The Programming Mode switch is used to update the firmware. For normal operation, it should be set to

JTAG.

1.3 Power

To apply power to the ADS1x31REF, connect a 9V battery or plug in a 6V–9V ac wall adapter.

AC adapters must be tip positive/sleeve negative. When an ac adapter is plugged in, the board always

takes power from it, and not from the battery.

The ADS1x31REF is protected against polarity reversal. If a power source is connected in reverse by

mistake, the display remains blank. To prevent damage to the board, do not leave a reversed power

source connected for longer than a few seconds.

1.4 Connecting a Load Cell

The ADS1x31REF is specifically designed for connection to load cells. Two connectors are provided for

this application. The terminal block is used for load cells having stripped wire connections; the load cell

header is for load cells having a header connector. The terminal block provides connections to the

reference input (or power supply) and the header has switched excitation.

1.4.1 Connecting a 4-Wire Load Cell to the Terminal Block

Figure 2 shows the connection of a 4-wire load cell to the terminal block. In this configuration, the load cell

is excited by the +5V power supply, and the ADC reference is taken from the power supply.

For this configuration, the reference select switch must be in the +5VA position.

Figure 2. 4-Wire Load Cell to Terminal Block

ADS1131REF and ADS1231REF SBAU175A–July 2010–Revised August 2011

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EXC-

SNS-

SNS+

SIG+

SIG-

EXC+

OUT+

EXC-

SENSE-

OUT-

SENSE+

EXC+

OUT+

EXC-

OUT-

EXC+

OUT-

EXC+

OUT+

EXC-

SENSE+

SENSE-

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Getting Started

1.4.2 Connecting a 6-Wire Load Cell to the Terminal Block

Figure 3 shows the connection of a 6-wire load cell to the terminal block. In this configuration, the load cell

is excited by the +5V power supply, and the ADC’s reference is taken from the sense wire returning from

the load cell. The sense wire connects to the excitation wire at the bridge sensor.

Figure 3. 6-Wire Load Cell to Terminal Block

1.4.3 Connecting a 4-Wire Load Cell to the Header

Figure 4 shows the connection of a 4-wire load cell to the header. In this configuration, the load cell is

excited by the +5V power supply, and the ADC reference is taken from the power supply.

Figure 4. 4-Wire Load Cell to Header

For this configuration, the reference select switch must be in the +5VA position; the EXT position does not

work.

1.4.4 Connecting a 6-Wire Load Cell to the Header

Figure 5 shows the connection of a 6-wire load cell to the header. In this configuration, the load cell is

excited by the +5V power supply, and the ADC reference is taken from the sense wire returning from the

load cell. The sense wire connects to the excitation wire at the bridge sensor.

Figure 5. 6-Wire Load Cell to Header

For this configuration, the reference select switch should be in the EXT position for best performance. The

+5V position also works, but the device may not perform as well.

SBAU175A–July 2010–Revised August 2011 ADS1131REF and ADS1231REF

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1.5 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.

1.6 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.

1.7 Common Tasks

1.7.1 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 RMS.

5. While still holding down DISP, press the UNIT button until the word on the right side is VOLT.

6. Release the DISP button. The display shows the word GOT 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.

1.7.2 Measuring Mass

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 SBAU175A–July 2010–Revised August 2011

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Part #	897-43-004-90-000000
Description	CONN RECEPT USB TYPE B PCB
Category	SOCKET
Availability	Out of Stock
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897-43-004-90-000000

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