STM32+MAX6675+K-type thermocouple temperature measurement

chloebb

STM32+MAX6675+K-type thermocouple temperature measurement [Copy link]

When using stm32+max6675+k-type thermocouple to measure the temperature of the transistor, the temperature can be displayed normally. However, when the Agilent power supply applies 0.1a current to the transistor and 5v voltage to the transistor, the current test temperature is displayed as zero degrees. The Agilent power supply is not in direct contact with the max6675, and it is suspected that interference has occurred, but there is no clue.

chunyang

The thermocouple and the transistor must be insulated. If they are connected, the temperature measurement circuit will naturally be affected when the transistor is energized.

chloebb

chunyang posted on 2020-7-30 18:42 The thermocouple and the transistor must be insulated. If they are connected, the temperature measurement circuit will naturally be affected when the transistor is powered on.

I have ensured that there is no connection between the thermocouple and the transistor, but the temperature is still abnormal and lower than the actual temperature value. I suspect that the max6675 is interfered with.

chunyang

chloebb posted on 2020-7-31 13:24 I have ensured that there is no connection between the thermocouple and the transistor, but the temperature is still abnormal and lower than the actual temperature value. I suspect that the max6675 is interfered with...

Try unified power supply, the two circuits should share the same ground. If the two circuits are independent and connected by a long line, interference may be induced through distributed capacitance coupling, mainly grid induction. If this is the case, your temperature measurement system must be reliably connected to the ground.

chloebb

Thanks man, I'll give it a try!!

guitianxia

It's been a while now, so it should be debugged...

If you need this kind of temperature measurement, I recommend MAX31856, which is more stable than max31855K max6675 and has much stronger anti-interference.

guitianxia

MAX31856 Key Features

Provides high-precision thermocouple temperature readings

Includes automatic linearity correction for 8 types of thermocouples

±0.15% (maximum, -20°C to +85°C) thermocouple full-scale and linearity error

19-bit, 0.0078125°C thermocouple temperature resolution

Built-in cold junction compensation to minimize system component count

The converter has a temperature resolution of 0.0078125°C.

Allows readings of temperatures from -210°C to +1800°C and as low as (depending on thermocouple type)

±0.7°C (max, -20°C to +85°C) cold junction compensation accuracy

±45V input protection, reliable system performance

Simplify system fault management and diagnostics

Detecting an open thermocouple

Over-temperature and under-temperature fault detection

50Hz/60Hz noise suppression filtering to improve system performance

14-pin TSSOP package

guitianxia

MAX31855 Key Features

Cold Junction Compensation

14-bit, 0.25°C resolution

The temperature resolution of the converter is 0.25°C.

Temperature readings from -270°C to +1800°C,

For K-type thermocouples, ±2°C accuracy is maintained over the -200°C to +700°C temperature range.

K, J, N, T and E thermocouple device versions available

Simple SPI compatible interface (read only)

Detects thermocouple shorts to GND or VCC

Detecting an open thermocouple

application

Electrical equipment

car

HVAC

industry

guitianxia

MAX6675 Key Features

Cold junction temperature compensation

12-bit, 0.25°C resolution

Can read temperatures from 0°C to +1024°C,

The thermocouple has an accuracy of 8 LSB over the 0°C to +700°C temperature range.

Simple SPI-compatible serial interface

Open Thermocouple Detection

The MAX6675 is available in a small, 8-pin SO package.

application

Electrical equipment

HVAC

industry

yf_gao

When I use MAX6675 to measure temperature, because my circuit board is placed inside the machine, the internal temperature will gradually rise, resulting in inaccurate temperature measurement by the thermocouple. For example, the temperature measured at room temperature is about 2° different. As the temperature rises, the difference becomes larger and larger. How can I solve this problem?