[PIC] interfacing j type thermocouple to PIC16F877

[pranav.itraj@gmail.com]

hi

i need help for
To interface J type thermocouple to PIC16F877 and also want to display it to the lcd16X2 display.
i want to use inbuilt ADC for the analog to digital conversion of given thermocouple.

 

[KlausST]

Hi,

thermocouple measurement is a relative measurement referenced to the so called "cold jucntion" thermocouple.
Therfore you additionally need the absolute temperature of the cold jucntion.

J type voltage is relatively good linear to temperature. Check if this is sufficient for you.

There are signal conditioning circuits for thermocouple (with built in absolute temperature measurement)
www.analog.com and www.linear.com and other manufacturers.

low pass filter before ADC reduces noise.


Signal path:
Thermocouple, analog signal conditioning, LPF, ADC conversion, offset correction, gain correction, printf() (or binary to BCD conversion, BCD to ASCII conversion)
should work.

Klaus

 

[pranav.itraj@gmail.com]

sir can you provide circuit diagram for it.

 

[paulfjujo]

hello,

Analog Device AOP :

Pretrimmed for Type J (AD594) or Type K (AD595) Thermocouples Can Be Used with
Type T Thermocouple Inputs Low Impedance Voltage
Output: 10 mV/8C
Built-In Ice Point Compensation
Wide Power Supply Range: +5 V to 615 V
Low Power: <1 mW
typical Thermocouple Failure Alarm
Laser Wafer Trimmed to 18C Calibration
Accuracy Setpoint Mode Operation
Self-Contained Celsius Thermometer Operation
High Impedance Differential Input Side-Brazed DIP or Low Cost Cerdip

AD594 output = (Type J Voltage + 16 µV) × 193.4
AD595 output = (Type K Voltage + 11 µV) × 247.3

if you have a power supply of 12V or 24VDC , you can also use
Thermocouple converter auto powered by the power supply, deliver 4-20mA for the full scale output
just insert a 250 ohms resistor to get 1-5V for PIC ADC input..