Ospid tc read problem, my input says error a lot

[kingbacana]

#3642

Hey Guys

I have a serious error, my input drops sometimes random

thats really bad in my way of using the ospid..

I used some log from serial monitor added some checks

in the code I printed out the max cpp file when read thermocouple:

It prints this: temperature = FAULT_SHORT_GND;

I tryed 4 thermocouple, what is dead on the ospid?

let me know plz

here is the code I used:
double MAX31855::readThermocouple(unit_t unit)
{
unsigned long data;
double temperature;

Serial.println(“max read:”);
// Initialize temperature
temperature = 0;

// Shift in 32-bit of data from MAX31855
data = readData();

// If fault is detected
if (data & 0x00010000)
{
// Check for fault type (3 LSB)
switch (data & 0x00000007)
{
// Open circuit
case 0x01:
temperature = FAULT_OPEN;
Serial.println(“fault open”);
break;

// Thermocouple short to GND
case 0x02:
temperature = FAULT_SHORT_GND;
Serial.println(“SHORT GND”);
break;

// Thermocouple short to VCC
case 0x04:
temperature = FAULT_SHORT_VCC;
Serial.println(“SHORT VCC”);
break;
}
}
// No fault detected

[rocketscream]

#4072

Is your thermocouple tip touching the ground or chassis made of metal which is connected to the system ground?

[kingbacana]

#4073

Thanks for your reply I really appreciate it 🙂

I checked all that, that isnt the issue 🙂

Do you have a power flow diagram or manual for checking voltages that lead from controller chip 2 t.c reading, so I can measure and check all those components?

I really need the ospid in a working state, 🙂

[kingbacana]

#4074

How to test if the temp chip that max chip is bad?

Also does the ospid have warranty??

Cause I checked on site, but new ospid cant buy its always out of stock, And I want to fix this ospid , cause need it, Payed for ospid and its not working? , why no chip protection?

whats happening??

[reserve]

#4075

I have the same problem as you have. I already checked the ospid for poor solder points and tried out 5 different thermocouples.
But i found nothing, the error is still there.
I did a small workaround in the firmware, and I hope that works (didn´t debug/test yet)

double readThermistorTemp(int voltage)

{

static double oldTemp = -999;

static int cnt = 0;

float R = REFERENCE_RESISTANCE / (1024.0/(float)voltage - 1);

float steinhart;

steinhart = R / THERMISTORNOMINAL;     // (R/Ro)

steinhart = log(steinhart);                  // ln(R/Ro)

steinhart /= BCOEFFICIENT;                   // 1/B * ln(R/Ro)

steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)

steinhart = 1.0 / steinhart;                 // Invert

steinhart -= 273.15;                         // convert to C



//eliminate big measurement error peaks

if((oldTemp != -999) && (abs(oldTemp - steinhart) > 10) && (cnt < 5))

{

steinhart = oldTemp;

cnt++;

}

else

{

cnt = 0;

oldTemp  = steinhart;

}



return steinhart;

}

[Cracked]

#4076

I have had this issue a few times. Its always been because my TC was grounded.

Also, don’t use the power supply while you have the osPID connected to a pc via the usb.

[kingbacana]

#4077

That code works only for Thermistor, T.C is digital , thermistor is analog 🙂 thanks for the try though,

A friend of mine has a usb logic analyzer he tested the max31855 chip and that chip is sendingbullshit we suspect faulty max chip.
So something burned that chip, maybe overcurrent with disconnecting and connecting usb,

I only used SSR on it and uploaded very often new firmware cause Im building new firmwre versions for test, somehow the chip is malfunction

Maybe ospid devteam need to overlook the hardware and built in some protection to prevent?

🙂 , its not a grounding issue with or on t.c , I tested this 😉

[reserve]

#4078

I replaced the MAX31855 chip today and finally I´m not getting any input errors at all. Seems that the chip was broken…

[rocketscream]

#4079

Hi guys,

Thank you for the report. I will look into this.

As far as we know, the one issue with MAX31855KASA+ was Maxim manufacture and deliver a bunch of wrongly trimmed chip out (temperature reading was lower than actual). That was sorted out few months back by sending replacement units to affected users. If you didn’t get any email, that means your chip is okay.

[kingbacana]

#4080

Great, but I never received a email about it, so I guess my version is good, but still not working?

what can cause the chip to die?

If I buy this one http://www.hobbyelectronica.nl/product/thermocouple-amplifier-max31855/?added-to-cart=5247
how to connect it or do I need to unsolder the chip from it and put it on the ospid pcb?

🙂 thank you

edit:
which will work better?
MAX31855KASA vs MAX6675ISA

on ospid site it says model now use max6675 and there is a line through the max31855?

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