What is a PID?
PID stands for Proportional Integral Derivative. It’s a digital temperature controller.
For an espresso machine, imagine your boiler heats up. How can the machine detects that it is too hot and stop heating or heating up further if it’s getting cold?
In most cases, a pressurestat controls the boiler’s temperature 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.
- More precise control of the temperature
- 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 from the same coffee at different temperatures and controlling the intensity of its bitterness and sourness. Personally from our 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 temperature fluctuation in the boiler, switching on and off according to the measured pressure. The PID is more reactive and will keep the deadband smaller, making the temperature more stable.
Here is an example of PID versus Pressurestat.
If 90°C is the set temperature, a PID may sway around 0.2°C up and down, and a pressurestat may sway approximately 2°C or more.
Which is more durable?
Pressurestats should last many years depending on the water condition, power stability and ambient temperature. In some models, they come with a version with heavy-duty pressurestats with higher resistance with longer expected longevity. We usually see pressurestats failing from limescale blockage than the component malfunctioning by itself. As such, it’s essential to have the water adequately softened to last 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 constantly switches on and off to regulate the machine’s temperature. Over time, the relay’s contact points can be corroded, making them no longer effective. The lifespan of the relay largely depends on the ambient temperature, the usage duration and power stability. It is good to replace it regularly if you want to be more assured. They are not that expensive. Having them switched on all the time is also not a good idea.
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 significant advantage it has is the solid-state relay can last much longer. The regulator and display may be more susceptible to moisture or power surge damage, 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 degrees Celsius. 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 need the PID? You decide.
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