ADI AD7793热电偶测量系统解决方案

ADI公司的 AD7792/3是高精度测量系统的低功耗低噪音模拟前端(AFE),包括三个差分模拟输出的低噪音16/24位Delta-Sigma ADC,仪表放大器能直接连接到ADC,增益设定为64,4.17Hz的噪音为40nV,工作电压2.7-5.25V, 主要用在热电偶测量,RTD测量,气体分析,工业过程控制,手持仪表,血液分析以及6位DVM等.本文介绍了AD7793主要特性,方框图, RTD和热电偶测量电路图以及采用AD7793 24位Sigma-Delta ADC完整的热电偶测量系统电路图和材料厂清单.

The AD7792/AD7793 are low power, low noise, complete analog front ends for high precision measurement applications. The AD7792/AD7793 contain a low noise 16-/24-bit Σ-Δ ADC with three differential analog inputs. The on-chip, low noise instrumentation amplifier means that signals of small amplitude can be interfaced directly to the ADC. With a gain setting of 64, the rms noise is 40 nV when the update rate equals 4.17 Hz.

The devices contain a precision low noise, low drift internal band gap reference and can accept an external differential reference. Other on-chip features include programmable excitation current sources, burnout currents, and a bias voltage generator. The bias voltage generator sets the common-mode voltage of a channel to AVDD/2.

The devices can be operated with either the internal clock or an external clock. The output data rate from the parts is software-programmable and can be varied from 4.17 Hz to 470 Hz.

The parts operate with a power supply from 2.7 V to 5.25 V. They consume a current of 400 μA typical and are housed in a 16-lead TSSOP package.

AD7793主要特性:

Up to 23 bits effective resolution

RMS noise

40 nV @ 4.17 Hz

85 nV @ 16.7 Hz

Current: 400 μA typical

Power-down: 1 μA maximum

Low noise programmable gain instrumentation amp

Band gap reference with 4 ppm/°C drift typical

Update rate: 4.17 Hz to 470 Hz

3 differential inputs

Internal clock oscillator

Simultaneous 50 Hz/60 Hz rejection

Programmable current sources

On-chip bias voltage generator

Burnout currents

Power supply: 2.7 V to 5.25 V

–40°C to +105°C temperature range

Independent interface power supply

16-lead TSSOP package

Interface

3-wire serial

SPI®, QSPI™, MICROWIRE™, and DSP compatible

Schmitt trigger on SCLK

AD7793应用:

Thermocouple measurements

RTD measurements

Thermistor measurements

Gas analysis

Industrial process control

Instrumentation

Portable instrumentation

Blood analysis

Smart transmitters

Liquid/gas chromatography

6-digit DVM

图1.AD7793方框图


图2.采用AD7792/3的RTD应用电路图

图3.采用AD7792/3的热电偶测量电路图

采用AD7793 24位Sigma-Delta ADC完整的热电偶测量系统

Complete Thermocouple Measurement System Using the AD7793 24-Bit Sigma-Delta ADC

The circuit, shown in Figure 4, is a complete thermocouple system based on the AD7793 24-bit sigma-delta ADC. The AD7793 is a low power, low noise, complete analog front end for high precision measurement applications. The device includes a PGA, internal reference, internal clock, and excitation currents, thereby greatly simplifying the thermocouple system design.

图4.带冷端补偿的热电偶测量系统电路图(简化电路图:所有的连接和去偶电容未标)

图5. 热电偶测量系统外形图
CN206热电偶测量系统材料清单见:

XY
Assembly
Report
for
ad7793
thermocouple
demo
a.pcb
on
05/07/2004NamePart
TypeValueTolerancePCB
DecalSMDPart
DescriptionStock
CodeBAT1BATT_COINBATT_COINNo2
Cell
20mm
Coin
battery
HolderDigikey
BH800S-NDC1CAP10nF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
301-9561C2CAP10nF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
301-9561C3CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C4CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C5CAP+10uFCAP\TAJ_AYesTantalum
Capacitor
-
TAJ
Series
(6.3V)FEC
197-014C6CAP+10uFCAP\TAJ_AYesTantalum
Capacitor
-
TAJ
Series
(6.3V)FEC
197-014C7CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C8CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C9CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C10CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C11CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C12CAP0.1uF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
499-675C13CAP10nF0603YesX7R
SMD
0603
Ceramic
CapacitorFEC
301-9561D1DIODED1MELF3YesGENERIC
DIODE
W
ALTERNATEBAV103DICT-NDJ1THERMOCOUPLETHERMOCOUPLENoMiniature
Thermocouple
ConnectorOmega
PCC-SMP-U-50-RJ2JUMPERSIP-2PNoJUMPER
BLOCK,
2
PINS
0.1"
SPACINGNot
InsertedJ3JUMPERSIP-2PNoJUMPER
BLOCK,
2
PINS
0.1"
SPACINGNot
InsertedJ4HEADER04SIP-4P-RANo4
Pin
90º
Single
Row
Surface
Mount
HeaderFEC
148-534
(36
Pin
Strip
-
purchase
1
strip
per
9
boards)R1RES1k+/-
1%0603Yes0.063W
ResistorFEC
911-239R2RES1k+/-
1%0603Yes0.063W
ResistorFEC
911-239R3THERMISTOR1950r-1990rTO-92-MODIFIEDNoThermistorPhilips
(Arrow)
KTY81/110R4RES2K0.10%0805YesPrecision
ResistorFEC
554-297R8RES1k+/-
1%0603Yes0.063W
ResistorFEC
911-239R6RES1k+/-
1%0603Yes0.063W
ResistorFEC
911-239R7RES82k+/-
1%0603Yes0.063W
ResistorFEC
911-460R5RES1R5+/-
5%0603Yes0.063W
SMD
ResistorFEC
758-267U1AD7792/93TSSOP-16YesLo-Power
16/24
Bit
Sigma
Delta
ADCAD7793BRUU2ADUC832LFCSP-56YesMicroConverter,12
bit
ADCS
and
DACSADuC832BCPU3MM5483PLCC44YesLCD
DriverNat
Semi
MM5483VU4VI509-DP_RC-SDIP40-1200NoLCD
4.5
Digit
.4"
Refl
w/dataDigikey
153-1025-NDS1SW-PUSH-SMDSW_PB_SMD_6MMYesSMD
Push
Button
Switch
(sealed
6mm
x
6mm)FEC
177-807Y1XTAL1_SMD32.768KHzXTAL_85SMXYesCrystalFEC
316-0312Placed
in
coin
cell
holder
&
isolated
using
paper.Pair
of
3V
20mm
Coin
Batteries
(CR2032)FEC
300-445
(x2)Packed
in
Eval
kit
box.T-Type
ThermocoupleFEC
410-0750Placed
in
underside
of
PCBRubber
Stick-on
feet
x4Stuck
on
Front
of
Eval
Kit
box.Barcode
LabelAnti-static
BagEval
Kit
Box详情请见:
48449和
48450