Analog Input App Notes
A common question is "can this sensor/signal be measured with a LabJack". Unless the signal has a voltage (referred to the device's ground) beyond the device's limits, it can be connected without damaging the LabJack. However more thought is required to determine what is necessary to make useful measurements with a LabJack or any measurement device.
A few important factors should be considered to be sure that you don't harm the device and get useful information.
Signal Voltage
Signal's Source Impedance
A Device's Resolution (and Accuracy)
Speed
Signal Voltage
Whether you are trying to make single-ended analog readings, differential analog readings (if your device permits), or fully isolated analog readings (our newflagship device, the T8), you need to make sure that the voltage on each channel with respect to ground (shared or isolated) is still within the common mode limits. When measuring parameters other than voltage, or voltages too big or too small for a particular LabJack, some sort of sensor or transducer is required to produce the proper voltage signal. Examples are a temperature sensor, amplifier, resistive voltage divider, or perhaps a combination of such things.
Notable piece of information:
Our U6 & T7 devices feature Fully-Differential Inputs that output calibrated voltage readings.
Our new T8 device features 8 Isolated Analog Inputs with simultaneous sampling.
Impedance:
When connecting a LabJack (or any measuring device) to a signal source, it must be considered what impact the measuring device will have on the signal. The main consideration is whether the currents going into or out of the device's analog input will cause noticeable voltage errors due to the impedance of the source. To maintain consistent results reference the appropriate device's datasheet (see below) or Users Guide Appendix A for the recommended maximum source impedance. Our devices have relatively high input impedance. However, in some very low current applications problems may arise.
Resolution (and Accuracy)
Each LabJack device has its own specifications regarding how precise and accurate they are. Please refer to the relevant LabJack datasheet (see below) or Appendix A for more information.
Speed
Speed is an important attribute when trying to acquire analog signals. If you are trying to read steady state signals (constant voltages like those given by potentiometers) its fairly straight forward. However, if you are trying to read and interpret a waveform it is much more complicated. Some of the information needed is the frequency, amplitude, offset, and a knowledge of what you expect to see (its shape). Answers to these questions will help decide how fast you need to collect data points and determine how complicated your code will need to be. Our LabJack devices have two general data acquisition modes, normal mode (command and response) and streaming mode (configuration and listening, a periodic bulk transfer of data). It is also important to consider how many channels you are expecting to read and if you are trying to read them simultaneously. Most of our devices use dedicated ADCs with analog MUXs to switch between input channels (Very common in the world of electronics). This means that there is a delay in-between "multiple channel reads" called scan rate.