What sensors are used in pizza ovens and prep areas?

Sensors monitor the temperature of pizza ovens and preparation (prep) areas. They also monitor and control the speed of pizza movement in conveyor ovens. A variety of sensor technologies are used in specific types of pizza ovens and for specific purposes.

This article briefly reviews the U.S. Food and Drug Administration (FDA) Food Safety Modernization Act (FSMA) sensor requirements. It then looks at common temperature sensor technologies used in pizza ovens and sensors used to monitor the temperature of prep areas. Finally, it looks at the types of motion sensors used in conveyor ovens.

FSMA includes the requirement that food facilities have a food safety plan and preventative controls based on process management. Process control for pizza restaurants includes operations like refrigeration, preparation, and cooking pizzas. Temperature and speed sensors can be key elements in pizza process control.

Thermocouples are common sensors used for monitoring oven temperature. They are low-cost, have high-temperature limits and wide temperature ranges, and are durable. Thermocouples are based on two wires of different metals coupled together (usually welded) on one end to form a junction. When the junction is exposed to temperature changes, it produces a voltage proportional to the temperature change.

Various metal pairs are used to form thermocouples; some can measure temperatures of thousands of degrees. Type K thermocouples made with Nickel-Chromium or Nickel-Alumel are commonly found in conveyor and deck-style pizza ovens. They typically have accuracies of ± 2.2 °C or ± 0.75%, whichever is greater, and are available in two grades rated for different temperature ranges:

Thermocouple grade with a temperature range of -454 to 2,300 °F (-270 to 1260 °C)
Extension grade with a temperature range of 32 to 392 °F (0 to 200 °C)

Electric or gas pizza oven temperatures can be as high as 260 °C and can be measured using extension grade Type K thermocouples. Those thermocouples are available with stainless steel, glass, or ceramic sheaths. Stainless steel probes provide the ruggedness needed in pizza ovens, and glass can also be used. Ceramic is less expensive but will corrode and must be replaced every year or two.

Figure 1. Typical thermocouple sensor with a stainless-steel sheath for a conveyor-style pizza oven. (Image: *Middleby*)

Wood-fired pizza oven temperatures can be over 370 °C, and inert gas-actuated oven thermometers rated up to 1,100 °C (600 °C) can be used. These sensors use an inert gas, such as nitrogen or argon, to transmit thermal energy from the sensing element to the temperature measurement system.

Thermometer guns

Infrared (IR) “thermometer guns” provide a non-contact way to monitor the temperature of pizza ovens from outside, especially with wood-fired ovens. These IR thermometers are available in rugged designs. For example, they can have an ingress protection (IP) rating, according to the International Electrotechnical Commission (IEC) 60529, the degree of protection standard of IP54. That indicates protection from dust and that exposure to dust won’t interfere with their operation. They are also protected from water splashing from all directions (Figure 2). Common features include:

Temperature range of -30 to 650 °C
Accuracy of ±1.0 °C or 1.0% of reading, whichever is greater
Memory can hold up to 99 measurements
Can display the minimum, maximum, or average temperature or the difference between two readings
Measurement time under 0.3 seconds

Figure 2. This IR thermometer gun can monitor pizza oven temperatures in various industrial applications. (Image: *Instrument Choice*)

Measuring cold

Negative temperature coefficient (NTC) thermistors monitor the temperature of refrigerated prep tables. An NTC thermistor is a thermally sensitive resistor whose resistance declines at a predictable rate as the temperature rises.

NTC thermistors are available and rated for temperatures from -40 to +110 °C. Devices designed for use in pizza prep tables have an IP67 rating. They are dust-tight and protected from immersion in up to 1 meter of water for up to 30 minutes.

Measuring motion

Hall effect and optical speed sensors are found on conveyor-type pizza ovens. Optical sensors use an infrared LED and measure the light reflected or interrupted by a rotating disk on the shaft of the conveyor drive motor. They can be subject to interference from contaminants and experience mechanical wear, and they have been largely replaced by Hall effect sensors.

Hall effect sensors are sealed, non-contact sensors that use magnetic fields to measure the rate of travel of pizza oven conveyors. A Hall effect sensor consists of a sensor circuit board and a multipole (often 8-pole) magnet. The magnet is placed on a rotating shaft connected to the conveyor, and the stationary circuit board senses the passage of the spinning magnet poles to determine the rate of speed.

Summary

Process monitoring and control are important aspects of the FDA’s FSMA requirements. To that end, a range of sensor technologies must be used to monitor pizza oven temperature, prep table temperature, and conveyor system speed.