Datasheet

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APPLICATION EXAMPLES
Weigh-Scale System
Noise−Free Counts +
ǒ
2
(18.4)1)
Ǔ
ǒ
10mV
39mV
Ǔ
+ 177, 385
Thermocouple
Noise−Free Counts +
ǒ
2
BIT
Eff
Ǔ
ǒ
FS
LC
FS
AD
Ǔ
ADS1232
ADS1234
SBAS350F – JUNE 2005 – REVISED FEBRUARY 2008
Therefore:
Figure 42 shows a typical ADS1232 hook-up as part
With +5V supply voltage, 177,385 noise-free counts
of a weigh-scale system. In this setup, the ADS1232
can be expected from the ADS1232/4 with the
is configured to channel one input with a gain of 128
onboard PGA set to 128.
at a 10SPS data rate. Note that the internal oscillator
is used by grounding the CLKIN/XTAL1 pin. The user
can also apply either a 4.9152MHz crystal across the
CLKIN/XTAL1 and XTAL2 pins, or simply apply a
See Figure 43 for the ADS1232 in a thermocouple
clock to the CLKIN/XTAL1 pin. For a typical 2mV/V
application. In this example, a type k thermocouple is
load cell, the maximum output signal is approximately
used; the temperature range is from – 260 ° C to
10mV for a single +5V excitation voltage. The
+900 ° C when the gain is set to 64 to maximize the
ADS1232/4 can achieve 18.4 noise-free bits at
full input range of the ADS1232. R
1
and a
10SPS when the PGA = 128 (refer to Table 1 ). With
REF1004-2.5V are used to set the common-mode
the extra software filtering/averaging (typically done
voltage to 2.5V for ungrounded junction
by a microprocessor), an extra bit can be expected.
thermocouples. With a gain of 128, the ADS1232
input has a typical noise of 17nV
RMS
for extremely
high-resolution applications.
If either a wider temperature range application is
Where:
required (up to +1350 ° C, for example), or a grounded
junction thermocouple is used, pin 1 of the
BIT
EFF
= effective noise-free bits (18.4 + 1 bit
thermocouple can be grounded (see Figure 44 ).
from software filtering/averaging)
When the gain is set to 2, the ADS1232 input has a
FS
LC
= full-scale output of the load cell (10mV)
typical 500nV offset error and a noise level of
FS
AD
= full-scale input of the ADS1232/4 (39mV
270nV
RMS
, which is good for all kinds of low-voltage
when PGA = 128)
output sensors. Note that to calculate the actual
thermocouple temperature, the ADS1232 internal
temperature sensor can be accessed in order to
measure the cold junction temperature along with the
thermocouple reading.
24 Copyright © 2005 – 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS1232 ADS1234