Calibrating the temperature probe

jftroff · February 18, 2017, 2:09am

So I saw a few post about calibrating the temp probes. Mine are a few degrees out and I do need them to accurate. the link http://wiki.brewpi.com/index.php/Temperature_Sensor_Calibration seems to be dead. Does anyone know where I can find this info? - Thanks!

Elco · February 18, 2017, 7:14pm

A few degrees sounds impossible. If they are within factory spec, the maximum difference between two sensors can be 1C. They are ±0.5C accurate.

If you uninstall the sensors and then refresh the device list with ‘read values’ checked, what do they read?

jmark71 · February 18, 2017, 7:16pm

I used the way back internet archive and got the wiki page… I’d repeat the info here, but I think the wiki page sums it up better

https://web.archive.org/web/20160625025604/http://wiki.brewpi.com/index.php/Temperature_Sensor_Calibration

That being said, at least on the BrewPi legacy branch, the instructions don’t work… I managed to get one sensor to change a maximum of -0.225 but the update command won’t do anything for anything higher than that it seems… I need one of my sensors to be adjusted by ~1C (-1.54F) but it simply won’t do it.

Elco · February 18, 2017, 7:20pm

I’m wondering whether there might be a bug in legacy when the system is in Fahrenheit.
Please try setting the system to Celsius and then do the correction.

jmark71 · February 18, 2017, 7:29pm

That made it worse I switched to Celsius, ran h{v:1}… showed j=0 for i=1. Ran U{i:1,j:-0.855} to DROP the temp 0.855C but it set j to POSITIVE 0.125, raising the temp!

Where in the code is this feature - maybe I can take a look.

Elco · February 18, 2017, 7:44pm

github.com

BrewPi/firmware/blob/legacy/app/controller/DeviceManager.cpp#L342




void handleDeviceDefinition(const char* key, const char* val, void* pv)
{
	DeviceDefinition* def = (DeviceDefinition*) pv;
//	logDebug("deviceDef %s:%s", key, val);
	
	// the characters are listed in the same order as the DeviceDefinition struct.
	int8_t idx = indexOf(DeviceDefinition::ORDER, key[0]);
	if (key[0]==DEVICE_ATTRIB_ADDRESS)
		parseBytes(def->address, val, 8);
	else if (key[0]==DEVICE_ATTRIB_CALIBRATEADJUST) {
		temperature parsedVal;
		if (stringToTempDiff(&parsedVal, val)) {
			def->calibrationAdjust = fixed4_4(parsedVal>>(TEMP_FIXED_POINT_BITS - CALIBRATION_OFFSET_PRECISION));
		}
	}		
	else if (idx>=0) 
		((uint8_t*)def)[idx] = (uint8_t)atol(val);
}


bool inRangeUInt8(uint8_t val, uint8_t min, int8_t max) {

The calibration offset is not stored with the same precision, so the data is shifted here.
Maybe that’s the cause of the issue.

Please note that Arduino is not officially supported anymore.
It looks like the bug was fixed here:

But that was after 0.2.10

jmark71 · February 18, 2017, 10:34pm

I’m not following… the legacy branch actually has that same fix you mentioned. So shouldn’t I just be able to use that version 0.2.11 for my Arduino?

EDIT… okay… I see 0.2.11 never got built for the Arduino… is there any reason why I couldn’t build it in Atmel Studio and deploy that?

jftroff · February 19, 2017, 2:00am

I have a Photon on order. So I am going to wait and see if that makes them better. Forgive my non-Linux knowledge, but where do I type “U{i:3,j:-0.3}” in at? Is there a file I am suppose to change this in?

Also I am using the BrewPi in a glycol like setting (just cold water chilled by an aquarium chiller) where do I change the PWM setting? Again currently running legacy.

Thanks again!

Elco · February 19, 2017, 10:44am

0.2.10 was the last version released for Arduino as binary. I don’t know if 0.2.11 compiles without issues.

jftroff, I hope you don’t mean a bare photon. The photon version requires some peripherals on the board that a bare photon does not have.
The Arduino version does not use PWM and therefore isn’t a good fit for glycol, where you need short cycle times.

jmark71 · February 19, 2017, 2:41pm

Jftroff… to use the commands you need to access the serial interface of the arduino. The easiest way I found to do that was open up the Arduino IDE, make sure the correct serial interface is open and then access the serial monitor. I would make sure the brewpi script is stopped from the web interface before running the commands. Using the h command, you’ll get a list of the attached devices… find the one that matches your probe and use that ID (the i value) in your U command.

jftroff · February 21, 2017, 2:47am

I am getting the Particle Photon (Headers) WRL-13774 from SparkFun.

Also thanks for clarification of the Arduino IDE.

jftroff · February 21, 2017, 4:48am

So I did some more research, glad I just bought one Photon. If and when the BrewPi spark is multi chambered and can run glycol it would be totally worth it spending $100. So I will hold on to the Photon for now for my future purchase.

While I cannot use profiles in fridge mode, it is still better than just a Johnson controller and it does provide data with the chart.

I gotten to a point with brewing that the fridge takes too long to control the temp spike that fermentation causes. Having a coil of cold water does an outrageous job of controlling the temp and keeping the beer stable.

I know a lot of brewers are making chillers and looking for ways to control them. The BrewPi would be a great tool. I know you have stated your working on it and I am looking forward to it.

Cheers!