Do I really need a PID temperature controller?

What is a PID?

Imagine your boiler heats up, how can the machine detects that the machine is too hot and stop heating or heats up further if it’s getting cold?

In most cases, a pressurestat controls the temperature of the boiler by detecting the amount of pressure it has. When it’s too high or too low, it will send a signal to the heating element to react accordingly.

A PID is a digital temperature controller that replaces the pressurestat. It measures the temperature of the water in the boiler directly and switches on and off as needed.

A PID has two additional features over the pressurestat.

  1. A more precise control of the temperature
  2. Narrows the deadband of temperature fluctuation

The user can have more accurate control over the temperature and tune to his preference. This might be useful for exploring different flavours coming from the same coffee at different temperatures, as well as controlling the intensity of its bitterness and sourness. Personally from our own real-life taste tests, most baristas we have met can’t tell the difference with a few degrees of variance, must less among casual drinkers. So it’s hard to justify if having a PID to improve the extraction is true.

The pressurestat will create a fluctuation of temperature in the boiler, as it switches on and off according to the measured pressure. The PID is more reactive and will keep the deadband smaller, so the temperature is more stable.

Here is an example of PID versus Pressurestat.

PID Versus Pressurestat

If 90°C is the set temperature, a PID may sway around 0.2°C up and down, a pressurestat may sway approximately 2°C or more.

Which is more durable?

Pressurestats by themselves should last for many years depending on the water condition, power stability and ambient temperature. In some models, they come with a version with a heavy-duty pressurestats with higher resistance, with longer expected longevity. We normally see pressurestats failing from limescale blockage than the component malfunctioning by itself. As such, it’s important to have the water properly softened to last it longer.

Pressurestat does not work alone, it works with a power relay which cycles power to the heating element. The relay also has a lifespan as it switches on and off all the time to regulate the temperature of the machine. Over time, the relay’s contact points can be corroded which makes them no longer effective. The lifespan of the relay largely depends on the ambient temperature, the duration of usage and stability of power. It is good to replace it regularly if you want to be more assured. They are not that expensive. It is also not a good idea to have them switched on all the time.

PID, like the pressurestat, does not work alone. It usually works with a solid static instead of a mechanical relay, a display, a water probe and a regulator.

Some may deem that having more electronics increases the risk of failure. The big advantage it has is the solid state relay can last much longer. The regulator and display may be more susceptible to damage from moisture or power surge, and the water probe can malfunction from limescale buildup. Overall, we still think that PID is a safer choice which should last longer especially if the user intends to switch the machine on for a prolonged period.

For PID espresso machines, you must not set the temperature above the boiling point of 100-degree celsius. As it may trigger the safety control to trip and shut off the power completely, and you will have a problem. As you will need to remove the hood to rest the safety or send it back to the service centres.

Back to the question, do you really need the PID? You decide.

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