Thermocouple options and installation¶
Getting your thermocouple situation sorted out is often the most confusing part for those unfamiliar with these little devices. In reality, there are only a few things to make sure of when getting set-up. For the uninitiated, this can feel daunting and overwhelming. This document is meant to explain things in plain terms and describe your options.
Some of what below are snippets from a blog post where thermocouples are discussed in much greater detail. If you’d like to know the theory and details around thermocouples, feel free to indulge yourself at:
Every new RoastLog user will fall into one of two categories:
- You do have an existing thermocouple and it’s connected to a device which displays the temperature reading.
- You do not have an existing thermocouple
Thermocouples “types”¶
The questions which pops up over and over is: “What type of TC do I need”. Sometimes folks really mean “What size, shape and type of thermocouple do I need?”, but note that “type” has a special meaning in this context. Thermocouples can be made of different types metals. This designates which “type” they are. The two most popular are Type-J and Type-K. The RoastLog Data Bridge works exclusively with Type-K (we’re currently working on getting it to work with both). We’ve found that the vast majority of roasters who have TCs are running Type-J.
A couple of notes:
- The only difference between TC “types” is the type of wire they’re made from.
- You can’t use a Type-J with a device made for Type-K, and vice versa.
- Thermocouples cannot be “split” like you’d split speaker wire. That is, if you have one TC, you cannot connect it to two readouts.
How can you tell which type you have? Thermocouples are color coded, so you can look at the color of your wires or connectors and figure it out. The Omega chart of thermocouple color codes is quite handy. If you can’t see the individual wires, look at any of the connectors. Yellow means Type-K and black is Type-J.
Over-temp TCs¶
At a minimum, there should be one thermocouple installed in any modern roaster which is connected to some over-temperature circuitry. This is as a safety measure, designed to shut off the gas in the case that the roaster heat gets too high.
Warning
For safety reasons, you should never disconnect your over-temp thermocouple or any other components in that system.
Using an existing thermocouple¶
Most modern roasters come with at least one thermocouple which is connected to some type of digital readout/display. If you’re very lucky, this would be a Type-K and have a mini-connector. In that case, you could simple unplug the TC from your existing digital readout, plug it into the Data Bridge and be done. Typically, people have a Type-J which will not work with RoastLog.
If you’re in this situation, your best option is to get a dual-element thermocouple. This consists of one probe, with two thermocouples inside of it. One of these thermocouples would be Type-J, which would connect to your existing reader while the other one would be Type-K and connect to the RoastLog Data Bridge.
A drawing of a dual-element thermocouple. Inside a stainless steel housing would be two separate thermocouples. In this diagram, one is Type-J and the other Type-K.
A dual-element type J/K thermocouple. Note that there is one stainless steel probe. The Type-K connector is a mini-connector, on the right side of the photo. The Type-J thermocouple terminates in bare wires (red and white). These could be installed directly into a Watlow digital readout or something similar. The bare wires could also be connected to a Type-J mini connector and plugged into another digital readout.
These are the types of TCs we try to keep and recommend to our users who already have an existing TC they use.
Note
The TCs we keep on hand are 3/16” diameter by 4” long with 6’ of stainless steel over-braided wire. If you need different dimensions, or even different TC types, we can help you get what you need.
Brand new installation¶
Arguably the easiest and least complicated path is to install a brand new thermocouple into your roaster. This may sound extreme, but in reality it’s very straightforward. Nowadays, most roasters come with TCs installed already. Drilling a hole and installing a new TC side-by-side is simply a matter of
Installation location¶
The first question which comes up is where to install a new thermocouple. There is not really one definitive answer for this since roasters vary drastically between different makes and models. However, there is a general location which you should aim for regardless of the roaster. This can be best shown in a photo:
This is taken from a 1989 Diedirch IR7, and shows the location of a user-installed thermocouple.
In this photo, we can see that the drum rotate clockwise and creates a bean curtain approximated by the white shaded area. To get a good measurement of what the beans are experiencing, the thermocouple should be placed such that it’s well within the bean mass. It should be obvious from the photo that if the thermocouple was installed on the right side, there is a chance it’d be out of the bean mass if a smaller batch was done.
In this case, the TC was installed directly in the door. You don’t have to do this, but you should take into consideration the location of the curtain, drum rotation direction and location of the fins inside the drum.
It’s important to be aware of the drum fins since this is usually the limiting factor on where you can or can’t install the TC. Make sure to find a spot where you can install the TC 2-3” into the drum without hitting any fins while the drum is turning.
Drilling a hole¶
Once you’ve identified the location, it’s time to drill the hole. This hole will ultimately be tapped for a very specific size to accept the compression fitting which will hold the thermocouple into place. As such, you need the right size drill bit and tap. We happen to have a small stock of these as well.
A compression fitting, 1/8”-27NPT tap and matching drill bit.
Beyond the items above you’ll need a good drill, some muscle and a tap handle. I’ve personally used this exact equipment to drill through 1/2” steel. It takes some patience, but it can be done.
Again, we can supply these parts if needed.
Tapping threads¶
Once the hold has been drilled, it’s time to tap some threads. Resources on how to tap threads abound on the Internet. So, we’ll refer you there for details. A couple of notes we will give:
- Be patient. Forcing a tap can break it and leave it stuck in the roaster.
- Use cutting fluid
- Us a tap handle, not a wrench
A thermocouple probe with its compression fitting. The threads on the right will be installed into the threads you’re cutting.
Once the threads have been tapped, clean out the hole and install the compression fitting. Once that is in, slide the thermocouple in and tighten the outer fitting (left side of photo) which will hold the thermocouple in place.
