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Electric Brewery Temperature Sensors / Probes

If you have been researching electric brewing options with the idea of converting from gas or propane to electric you have probably been overwhelmed with temperature probe options. The two most common sensor available are Thermocouples and PT-100 RTD's. Both are stable, accurate temperature measuring devices. But what's the difference between the two? What are the advantage of each type?

  K Type Thermocouple PT100 RTD
Technology A thermocouple converts temperature into a small voltage that is fed back to your PID controller. Your PID controller converts this voltage into temperature, then uses the measured temperature to determine when to turn your heater on.

A RTD is a precision platinum resistor that changes value based on temperature. Your PID constantly reads the RTD's resistance and converts the value to temperature, then uses the measured temperature to determine when to turn your heater on.

K type thermocouples can be as far off as 4 degrees F at mash temperature of 145F. This is why if you are using a  K type thermocouple your PID must be calibrated before being used the first time. But once calibrated your measurements will be very repeatable - they will be the same over and over again. RTDs can also be off at mash temperature. Also wire loop resistance can add measurement error to a RTD. But a 3 wire RTD connection solves the loop resistance issue by factoring the resistance into the measurement.
K type thermocouples can tolerate series resistance (bad connections) much better than PT100 RTD's and when a connection gets bad enough they just stop working.  
Your PID must be calibrated before first use and re-calibrated any time you replace your thermocouple. RTDs are slightly more expensive than K type thermocouples and RTDs tend to have slower response time than K type thermocouples, but the difference probably won't be noticed in a home brewery.

So, what's the best sensor for your electric home brewery? Either will do a good job and a few years ago I would have said that a thermocouple will do a good job for less money. But cost for a good PT-100 RTD has been closing in and a PT-100 is an excellent choice providing you use a 3 wire connection.

Measuring and Monitoring Mash Temperatures

How you monitor your mash temperature depends more on what type of mashing you are doing than anything else. And since you can't measure every point in your mash tun you need to set-up mashing techniques that do a good job of mixing your mash so the temperature is even throughout your mash tun then pick a point to measure a good mash temperature average.

Direct Heat Temperature Considerations

The most important part of mashing with direct heat regardless of what type of heat you use is understanding that your mash tun always has a hot spot that you have to deal with. In the case of outside heat like a gas burner or stove top, that hot spot is the bottom of your mash tun. In the case of a element under your false bottom the hot spot is the heating element. With no intervention heat will travel slowly from your pot's hot spot and this means that the temperature of your mash right at the bottom of your pot will be much higher than the temperature of your mash mid-way up your pot. The temperature can be so extreme that you can scorch your mash while your sensor is still reading less than 145F! The only real defense for this is constant stirring to keep spreading heat through your mash.

Even with these challenges, with direct heat the best place to mount your sensor is about mid-way down the side of your pot because this is the best place to monitor your average mash temperature.

RIMS (Recirculating Infusion Mash System) Tube Temperature Considerations

With a RIMS tube your wort is passing through a confined space containing a heating element that was originally designed to bulk heat 30 to 50 gallons of water. This means that a RIMS tube can get hot in a hurry! A lot of "experts" will advise you to monitor the temperature leaving your mash tun but I believe this is dangerous to your mash. The problem is the temperature of the wort leaving your RIMS tube can easily be well above 170F while your average mash temperature and the temperature leaving your mash tun is still well below 145F!

  Maximum temperature rise through your RIMS Tube  
  Heating Element 1650 Watts 5500 Watts  
  BTUs / Hour 5,627 18,755 Element wattage X 3.41 BTU per watt hour
MARCH 809 Pump 7 GPM / 420 GPH Maximum flow rate - no restrictions
  Temperature rise 13 deg. F 45 deg. F BTUs per hour / 420 GPH with element on 100%
  MARCH 809 Pump 3 GPM / 180 GPH Worse case after false bottom and other restrictions
  Worse Case Temperature rise 31 deg. F 104 deg. F BTUs per hour / 180 GPH with element on 100%







So, what is this telling me?
With a MARCH 809 pump and a 5500 watt element turned all the way on, and with no flow restriction your wort temperature will rise 45 degrees F through your RIMS tube . With a MARCH 809 pump and a 5500 watt element turned all the way on, and with a 60% restriction your wurt temperature will rise 104 degrees F as it passes through your RIMS tube! And BTW, this is more real world because all RIMS systems have flow restrictions. In other words, use the temperature leaving your mash tun to run your RIMS tube and you risk over shooting your target mash temperature by a lot!

The reason for this is temperature adjustments will move through your mash in a wave. A 5 degree adjustment will take a very small amount of time to reach the top of your mash tun, more time to reach mid-way down your mash tun and even more time to reach the bottom of your mash tun. This is because it takes a certain amount of time for your wort to circulate through your system and a certain amount of time for your mash to absorb heat from your wort. It is a good idea to monitor the temperature leaving your mash tun to understand how long this cycle takes, just don't use this temperature to control your RIMS tube.

You have to use the temperature of the wort leaving your RIMS tube to control your RIMS tube! And BTW, a MARCH 809 pump even at 3 GPM provides more than enough circulation for a RIMS tube that's properly set up.

HERMS Temperature Considerations

With a HERMS system you are using the energy stored in your hot liquor tank sparge water to manage your mash temperature. The upside of HERMS is heating your sparge water and then using the water to heat your mash provides huge thermal buffer that smooth's out temperature changes. And unless you just aren't paying attention it's near impossible to over shoot your target mash temperature. But this huge thermal buffer also comes with a down side. Because you are changing the temperature of both your sparge water and your mash, step mash reaction time can be slower.

Just like RIMS you should be using the outlet temperature of your HERMS coil to manage your HERMS heater. If you decide to use the temperature mid-way down or the temperature leaving your mash tun you will see some temperature over-shoot. How much depends on how fast your circulation is running.

BIAB Temperature Considerations

From a temperature control point of view a BIAB system looks like a tightly controlled cross between a RIMS and a HERMS system. And because the circulation loop is so tight through BIAB you can place your temperature probe mid-way or at the bottom of your BIAB pot with no negative effect on your results. Most BIAB brewers place their temperature probe about mid-way down their BIAB pot. 

DS18B20 Temperature Sensors

A few people asked me why I did not cover the DS18B20 sensor in this article. These are really neat programmable sensors and their accuracy is excellent. But to use them you need at minimum a micro-controller and some programming knowledge. The programming skills needed are beyond most homebrewers abilities which is why the go-to controller for years has been a self contained PID module like my favorite, the MYPIN TA4 SNR controller. I compared the K type thermocouples and RTD's because these are the most common sensors used by homebrewers.

But in case you are curious the DS18B20 sensor is a self contained digital thermometer that communicates back to a controller or CPU through one wire. They need three wires total - power, ground and the one wire data connection. The neatest thing about these is each one is internally serialized and you can wire them in parallel then talk to each individually. I believe it's just a matter of time before the Chinese start producing PIDs with DS18B20 inputs. And when they do I'll be in line to buy a few!



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