The Raspberry Pi Foundation is a UK-based charity that works to put the power of computing and digital making into the hands of people all over the world. We do this so that more people are able to harness the power of computing and digital technologies for work, to solve problems that matter to them, and to express themselves creatively.

Raspberry Pi  is a bare bones PC for simple PC based projects that need more than a simple micro processor, but not a full blown PC.

It's small size lends to embedded systems.

The SD card OS tends to be Linux based.

It's built in GPIO ( general purpose inputs/outputs ) are suited for automation projects.

What it gives up are a hard drive, memory cards, and built in power supply.

Use the onboard USB connections to add keyboard, mouse, USB memory,. . .

A built in monitor connector and power supply connector complete the system.

Beginners should start with the NOOBS (New Out Of Box Software) operating system installation manager, which gives the user a choice of operating system from the standard distributions.

SD cards with NOOBS pre-installed should be available from any of our global distributors and resellers. Alternatively, you can download NOOBS.

Raspberry Pi OS (previously called Raspbian) is the recommended operating system for normal use on a Raspberry Pi.

Temperature Basics

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Temperature, pressure, & flow are the most used process measurements in industry.

As such there are many options to choose from.

For temperature in the process industry, 99% or more of the temperature loops use thermocouples or resistance temperature detectors (RTD). The RTD provides sensitivity (minimum detectable change in temperature), repeatability, and drift that are an order of magnitude better than the thermocouple.

Thermocouples are made up of 2 different metals that produce a voltage that varies with temperature.

That millivolt signal is then amplified for reading.

An RTD is a platinum resistor ( usually 100 ohms ) that varies with temperature.

 A circuit is required to measure that resistance and produce a voltage usually 0 to 5 VDC.

A 3 wire RTD is generally good, but a 4 wire will give the best accuracy with an extra cost.

Accuracy, Range, and Usability of Temperature Sensing Elements

Sensitivity and repeatability are two of the three most important components of accuracy.

The other most important component, resolution, is set by the transmitter.

Drift is important for extending the time between calibrations

Thermistors, which have seen limited use in the process industry despite their extreme sensitivity and fast (millisecond) response, primarily because of their lack of chemical and electrical stability.

Thermistors are also highly nonlinear, but this can be addressed by smart instrumentation.

Also of importance depending on the desired accuracy and repeatability is the effects of noise and calibration.

Determining which type of temperature sensor to use is based on:

1) Mounting - How will you physically mount the sensor to make your measurements ?

     For measuring air temperature in a clean environment, you can get away with using a thermistor or TMP36.

     For measuring a liquids temperature, you will need a protective probe type enclosure.( Usually RTD or thermocouple ).

2) Temperature range is another limiting variable. Too small a range will not work.

3) Accuracy needed.( See Temperature Noise & Calibration.txt )

Temperature Sensing Elements
 

Thermocouple

RTD (Pt 100 ) Thermistor
Repeatability 1-8 0.02-0.5 0.1-1
Drift 1-20 0.01 - 0.1 0.01 - 0.1
Sensitivity ( C ) 0.05 0.001 0.0001
Temperature Range ( C ) -200 to 2000 -200 to 850 -100 to 300
Signal Output (volts) 0-0.06 1 - 6 1 - 3
Power (watts at 100 ohm ) 0.4 2 0.4

NOTE: The TMP36 is a low voltage, precision centigrade temperature sensor. It provides a voltage output that is linearly proportional to the Celsius temperature. It also doesn't require any external calibration to provide typical accuracies of ±1°C at +25°C and ±2°C over the −40°C to +125°C temperature range.

NOTE: Thermocouples come in type of different bi-metal for different ranges.

The most common being J & K type.

J - 0 to 750°C

K - 0 to 1250°C

Some quick & simple Arduino solutions:

TMP 36 / DS18B20 ( Solid State )

These sensors use a solid-state technique to determine the temperature. They use the fact as temperature increases, the voltage across a diode increases at a known rate. (Technically, this is actually the voltage drop between the base and emitter - the Vbe - of a transistor.) By precisely amplifying the voltage change, it is easy to generate an analog signal that is directly proportional to temperature.

TMP36

Temperature range: -40°C to 150°C / -40°F to 302°F

Output range: 0.1V (-40°C) to 2.0V (150°C) but accuracy decreases after 125°C

A simple 3 wire connection.

#1) 2.7 to 5.5VDC VCC

#2) Analog voltage out (A0)

#3) GND

DS18B20

Uses the Dallas 1-Wire protocol, which is somewhat complex, and requires a bunch of code to parse out the communication, but avoids signal issues with long runs.

  • Usable temperature range: -55 to 125°C (-67°F to +257°F)
  • 9 to 12 bit selectable resolution
  • Uses 1-Wire interface- requires only one digital pin for communication
  • Unique 64 bit ID burned into chip
  • Multiple sensors can share one pin
  • ±0.5°C Accuracy from -10°C to +85°C
  • Temperature-limit alarm system
  • Query time is less than 750ms
  • Usable with 3.0V to 5.5V power/data

DHT22 ( thermister )

Good for 0-100% humidity readings with 2-5% accuracy

Good for -40 to 80°C temperature readings ±0.5°C accuracy

No more than 0.5 Hz sampling rate (once every 2 seconds)

This is a thermistor ( temperature sensitive varying resistor ) with a capacitor for humidity.

-200°C to +1350°C output in 0.25 degree increments - note that K thermocouples have about ±2°C to ±6°C accuracy

SPI data output requires any 3 digital I/O pins.

The MAX6675 performs cold-junction compensation and digitizes the signal from a type-K thermocouple.The data is output in a 12-bit resolution, SPI-compatible, read-only format.

RTD-Pt100

Usable temperature range: -200 to 550°C (-328°F to +1,022°F)

±0.5°C Accuracy from -10°C to +85°C

Platinum RTD Sensor - PT100 - 3 Wire

Resistor material is Platinum with a value of 100 ohm at temperature 0°C

Platinum has a positive resistance temperature factor; resistance increases with rising temperature

Resistance variation is a function of temperature: 0.385Ω/°C nominal

RTD to MAX31865 0-5VDC

Raspberry Pi Solutions

MCC 134 Thermocouple Measurement HAT

Provides four thermocouple inputs for adding temperature measurement capability to Raspberry Pi based systems. It features 24-bit resolution and provides professional-grade accuracy which is best in class. The MCC 134 also offers open thermocouple detection so users can monitor for broken or disconnected thermocouples and each channel type is selectable on a per-channel basis. Up to eight MCC DAQ HAT devices can be stacked onto one Raspberry Pi.

ESP8266_MQTT_Pi

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This is an example of using an ESP8266 via MQTT to a Raspberry Pi.

The wiring is similar to the other ESP MQTT Button examples with D7 pin 13 connected to a push button with Vcc on one side and a 1K resistor to GND.

The ESP publish code is similar to all the other IoT internet examples.

In this case though, we are going to use a Raspberry Pi as the MQTT broker (server).

The subscribe request will be issued by your PC via Putty.

This example does not use any user/password security.

Vast credit and thanks to www.instructables.com with a few upgrades and clarifications for the latest Raspberry Pi4 Buster version.

 

 

Tutorials

Here are some helpful tutorials on some the systems available with Scada123 to try on your own.

You can view videos at:     Youtube Channel Scada LLC

Sort through Topics on the left Menu "Tutorial Menu"

Click on one the Topic Tags that interest you.

License : All programs in the tutorial section are free software. You can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful,  but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.