Signal conditioners are devices that modify output signals produced by a sensor. These modifications are meant to help the monitoring devices better understand the signals from the sensors. Amplification, excitation, and filtering are few among the most popular types of signal conditioning.
Signal conditioners differ based on the physical value that it measures and also according to the type of features. Let’s discuss both the types in detail.
Types of Signal Conditioners According to Measurement
1. Temperature Signal Conditioner
A temperature signal conditioner is used with sensors that measure temperature or variations in temperature. Sensors that measure temperatures are called thermocouples. Usually, thermocouple outputs are in the range of plus or minus 80 mV.
Such a low output voltage is difficult for digital readers to record and display. This is where signal conditioners are helpful. These devices amplify the signals, filter the noise, and send it for further analysis/display.
Thermocouple Signal Conditioner
Apart from amplifying the signals generated by thermocouples, signal conditioning is also necessary for cold junction compensation. When a thermocouple is connected to the instrument for temperature measurement, the material difference between the two generates a voltage at junctions known as cold junctions. This voltage change affects the actual output of the thermocouple, giving out erroneous results.
A signal conditioner compensates for such variations and also filters out the power line noise. Additionally, the device also performs linearization so that the output voltage of the thermocouple is linear with temperature.
Thermistors Signal Conditioner
Thermistors require current and voltage excitation as these are active temperature sensors. Amplification and low pass filtering are also used for thermistors to modify the signals so that they can be easily read by the digital devices. A signal conditioner for the thermistor performs these operations effectively.
RTD Signal Conditioner
Resistance Temperature Devices or RTDs are temperature monitors that use the variation in resistance to calculate the temperature. Similar to thermistors, RTDs also require excitation voltage, amplification, and filtering. The RTD signal conditioner helps to meet such requirements while also eliminating unwanted signals from line resistance, non-linearity, and self-healing.
2. Pressure Sensor Signal Conditioner
Pressure sensing works by monitoring the strain or stress experienced by a bridge. The pressure signal conditioner excites the bridge by providing constant voltage and amplifying the output signals. The output of the pressure sensor varies in millivolts along with high common-mode signals.
The pressure sensor signal conditioner eliminates common-mode signals while retaining pressure variation values.
3. Load Cell Signal Conditioner
Strain gauges are extremely sensitive and they produce output in the range of millivolts. The load cell signal conditioner is necessary to pick up these small variations to ensure accurate measurement. Strain gauges also require excitation voltage in the range between 2.5V to 10V and this is achieved through a signal conditioner.
4. LVDT Signal Conditioner
Linear variable differential transformers or LVDTs measure the position of a subject. A sinusoidal excitation wave (between 400kz and 10 kHz) is required to excite the LVDT sensor. The output is then passed through a low pass filter to ensure that the noise levels are kept to a minimum. The final signal sent by the signal conditioner is easy to recognize for the digital reading device.
5. Torque Signal Conditioner
Torque signal conditioners follow the suite of the load and pressure signal conditioner as it can produce low or high output voltage based on the excitation voltage of the sensor.
6. Strain Gauge Signal Conditioner
Strain gauge signal conditioners require excitation voltage (around 10V) and amplification. The output of a standard strain gauge is in millivolts. A strain gauge signal conditioner modifies this output signal to scale it and make it readable for the modern digital recorders.
7. DC and AC Signal Conditioner
The choice between AC and DC signal conditioner is made based on the measurement setup. Resistance transducer setups like strain gauge use DC signal conditioners with amplification and filtering circuits.
AC signal conditioners are used in conjunction with variable reactance transducers and in setups where there is a considerable length between the transducers and the signal conditioning devices.
8. Frequency Signal Conditioner
Frequency signal conditioners or frequency transducers convert frequency into a standard output signal that can be easily measured using popular measurement devices.
Types of Signal Conditioners According to the Features
1. Universal Signal Conditioner
A universal signal conditioner is a device that can be programmed for multiple combinations of input/output configurations. From current, voltage, thermocouple, RTDs, and potentiometer to linear resistance signals, the device makes it easy to connect the most common sensors without requiring a separate signal conditioner for each. The device comes with a programmable module that allows configuring the signal conditioner for specific input/output requirements.
2. Multi-Channel Signal Conditioner
A multi-channel signal conditioner works similar to a universal signal conditioner allowing multiple input/output combinations. However, in the case of a universal signal conditioner, there is only one input and one output. Whereas, a multi-channel unit will have an option of 2 or more input/output.
3. Signal Conditioner and Isolator
A signal conditioner and isolator are often useful in applications where the signals from the source to the measuring device are required to be transmitted without a physical connection. Isolators also prevent undesirable ground loop currents and protect the control system from transients and electrical noise produced due to unpredictable field conditions.
4. Signal Conditioner Splitter
A signal conditioner splitter accepts one input signal and splits the output into two identical signals through two separate channels. These channels are isolated from each other and work independently. The isolation further helps in preventing ground loops and transient signals. These devices are useful in applications that require output measurement at two different areas from a single repeater base unit.