MAX31850 データシートの表示（PDF） - Maxim Integrated

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MAX31850

Cold-Junction Compensated, 1-Wire Thermocouple-to-Digital Converters

Maxim Integrated 

MAX31850/MAX31851

Cold-Junction Compensated, 1-Wire

Thermocouple-to-Digital Converters

Table 1. Thermocouple Wire Connections and Nominal Sensitivities

TYPE

K

J

N

R

S

T

E

T- WIRE

T+ WIRE

TEMP RANGE (°C)

Alumel

Chromel

Constantan

Iron

Nisil

Nicrosil

Platinum

Platinum/Rhodium

Platinum

Constantan

Platinum/Rhodium

Copper

Constantan

Chromel

-270 to +1372

-210 to +1200

-270 to +1300

-50 to +1768

-50 to +1768

-270 to +400

-270 to +1000

SENSITIVITY (µV/°C)

41.276

(0NC to +1000NC)

57.953

(0NC to +750NC)

36.256

(0NC to +1000NC)

10.506

(0NC to +1000NC)

9.587

(0NC to +1000NC)

52.18

(0NC to +400NC)

76.373

(0NC to +1000NC)

COLD-JUNCTION

SENSITIVITY (µV/°C)

(0NC TO +70NC)

40.73

52.136

27.171

6.158

6.181

41.56

44.123

Conversion Functions

During the conversion time, tCONV, three functions are

performed: the temperature conversion of the internal

cold-junction temperature, the temperature conversion of

the external thermocouple, and the detection of thermo-

couple faults.

When executing the temperature conversion for the inter-

nal cold-junction compensation circuit, the connection to

signal from the external thermocouple is opened (switch

S4) and the connection to the cold-junction compensa-

tion circuit is closed (switch S5). The internal T- reference

to ground is still maintained (switch S3 is closed) and

the connections to the fault-detection circuit are open

(switches S1 and S2).

When executing the temperature conversion of the

external thermocouple, the connections to the internal

fault-detection circuit are opened (switches S1 and S2 in

the Block Diagram) and the switch connecting the cold-

junction compensation circuit is opened (switch S5). The

internal ground reference connection (switch S3) and

the connection to the ADC (switch S4) are closed. This

allows the ADC to process the voltage detected across

the T+ and T- terminals. If T+ and T- are unconnected,

the thermocouple temperature sign bit is 0 (MSbit of

Scratchpad Byte 1), and the remainder of the thermo-

couple temperature value is 1.

During fault detection, the connections from the exter-

nal thermocouple and cold-junction compensation

circuit to the ADC are opened (switches S4 and S5,

see the Block Diagram). The internal ground reference

on T- is also opened (switch S3). The connections to

the internal fault-detection circuit are closed (switch

S1 and S2). The fault-detection circuit tests for shorted

connections to VDD or GND on the T+ and T- inputs,

as well as looking for an open thermocouple condi-

tion. Bits 0, 1, and 2 of the internal (cold junction)

temperature data are normally low. Bit 2 goes high to

indicate a thermocouple short to VDD, bit 1 goes high

to indicate a thermocouple short to GND, and bit 0

goes high to indicate a thermocouple open circuit. If

any of these conditions exists, bit 0 of the cold-junction

compensated thermacouple temperature data, which

is normally low, also goes high to indicate that a fault

has occurred.

Maxim Integrated

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