We often get questions about acquiring and recording biosignals using NI data acquisition products. While it may be possible in some cases and with some types of signals to directly acquire a signal with one of our products, it is not recommended. NI does not make any hardware that is designed for direct connection to ANY living organism. There are two big problems:
1. SAFETY - you need an isolated amplifier system with appropriate safety certifications (UL 60601-1 or EN60601-1) which is critical to provide protection against shocks and/or burns in the case of an electrical fault. And not just faults originating from the data acquisition system. You also need protection from providing a ground path for electrical faults originating from some other device that may come into contact with the subject. If you are trying to record from a frog or something, you may not care so much about safety, but then you have the next problem:
2. PERFORMANCE - surface biosignals (EEG, EMG, ECG, etc.) require specialized amplifiers to acquire cleanly. The signals are riding on top of 56/60Hz line frequency interference that is often orders of magnitude greater than the actual biosignal. The signals are also commonly riding on top of a large DC offset generated by the electrodes and electrolyte used to make a good connection with the skin, and the source impedance (electrode to skin/body) is high (5-10Kohms or more) and often badly mismatched. Signal conditioners for biosignals are designed specially to deal with these issues - they are usually AC coupled, have adjustable low and high pass filters (and often a notch filter at the line frequency) to block the offset potential and prevent noise from being digitized and aliased, have multiple stages of gain to reduce amplifier blocking (saturation) due to movement and other transients. Finally, they have very high impedance balanced inputs (high CMRR) to reject the common-mode noise and only amplify the signal of interest.
The good news is that specialized amplifiers are available from a number of sources and have high-level analog outputs that are ready to be digitized by almost any NI DAQ product.
Here are some good sources:
- Grass Technologies (www.grasstechnologies.com) - Grass specializes in neurophysiological recording systems and has a good selection of single and multi-channel amplifiers systems. Their equipment is extremely flexible, with a wide range of gains and filter settings. They sell a range of electrodes, sensors, and signal conditioners for handling many recording tasks involving both biosignals and other parameters involved in both in vitro and in vivo physiology studies (forces, pressures, etc.). Grass is also well know for their versatile stimulators, used for generating precisely timed pulses for nerve and muscle stimulation.
- World Precision Instruments (www.wpiinc.com) - WPI sells a wide variety of products, ranging from surgical instruments, to tubing and glassware, to amplifiers and data acquisition systems. They supply amplifiers that are suitable for both intracellular recording as well as extracellular and surface recording.
- Mindware Technologies (www.mindwaretech.com) - Mindware is an NI Alliance partner and provides turnkey data acquisition and experimental control systems, physiological data analysis software and custom laboratory integration services. They have a modular signal conditioning system (Bionex) and a range of LabVIEW based acquisition and analysis software tools.
- iWorx Systems (www.iworx.com) - iWorx manufactures and sells a line of amplifiers, data recorders, and sensors primarily for educational and research in animal and human physiology. Products such as the ETH-256C simplify acquisition of a variety of biosignals and transducers and have outputs that are easy to connect and directly compatible with a variety of NI DAQ products.
This is a start...as we build this list we can start to break them into logical categories and even allow group members to comment on their experience with some of the individual products.
Happy recording,
Steve
