How to Use Sensors to Convert Physical Quantities into Electricity?
Lesson 1 of Applying Data Acquisition System (DAQ)
The sensor (Sensor & Transducer) is the first unit of the data acquisition system architecture. Converting physical quantities (flow rate, stress, temperature, etc.) into electricity through different sensors is the first step in performing measurement.
Figure 1: Data acquisition system architecture
The heart of a modern data acquisition system is a high-precision multimeter (6 1/2 resolution). Voltage, current, resistance, and frequency are the basic measurement functions of a multimeter. As long as they can be converted into the above-mentioned electricity, the changes of these data can be measured, stored and analyzed by the data acquisition system for a long time.
Convert stress to resistance using strain gauges:
From the definition formula of resistance, we know that resistance is proportional to length and inversely proportional to cross-sectional area. Strain gauge applies the characteristic of resistance. When the strain gauge is stressed, it will cause the length to change, and the changed length will cause the change in resistance. By measuring the change in resistance, the stress can be converted into electricity (resistance).
Figure 2: Physical diagram of strain gauge (left), conversion principle (middle), resistance formula (right)
Convert flow rate into frequency through Hall sensor:
The simplest flow rate sensor consists of a plastic valve body, a rotor assembly (propeller) and a Hall sensor. When the air flow or water flow passes through, it drives the rotor (propeller) to rotate, and the Hall sensor outputs the corresponding pulse signal (frequency).
Figure 3: Schematic diagram of flow rate sensor
Temperature measurement derived from voltage and resistance measurements: The following conversions are common applications
Thermal Couple: Seebeck Effect converts temperature into voltage.
Thermistor: RTD or Thermistor converts temperature into resistance.
Figure 4: Thermocouple form, temperature measurement range and temperature-to-voltage conversion
In addition to the above-mentioned sensors, many sensors have output specifications of 0~5V, 0~10V, and 4~20mA. This type of application that converts into voltage or current is a more common sensor form.
Figure 5: Main functional specifications of GW Instek DAQ-9600 data acquisition system
GW Instek DAQ-9600 uses the GDM-9061 six-and-a-half-digit multimeter as its heart. The accuracy and distribution characteristics of GDM-9061 are comparable to those of the world's leading models. Please see Figure 6 for a comparison of related characteristics.
Figure 6: Red is GW Instek GDM-9061, blue is brand K 34461A
For more product information: www.gwinstek.com/en-global/products/detail/DAQ-9600
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