When It Comes To Data Acquisition Systems, Input Usually Winds Up In The Digital Realm.

When data acquisition systems first became standard in hospitals and labs around the world, the signal that was being gathered usually traveled through the system in an analog format up until the data was actually collated.  These days there are many benefits to having the signal in digital format as it moves through the system.

The first step in data acquisition starts with measuring something.  Whether it’s temperature or pulse rate there is a physical phenomenon or property of an object that must be measured and tracked.  Most data acquisition systems can handle a wide range of input but regardless of what is being measured the original source needs to be converted from a physical property into a corresponding measurable electrical signal. 

The transducer is the device that turns a physical property or phenomenon into a corresponding electrical signal that can be measured.  The measurements occur by comparing changing in the signal such as voltage, current, change in resistance or capacitor values etc.  The ability of the system to accurately measure the signals is key, and most signals are conditioned in order for the system to read them correctly.  This conditioning might be amplification or deamplification or any of the many other electrical adjustments that can be made to a signal.  
The reason that data acquisition systems starting to use a digital format for data traveling through the system is that as the original signal moves through the transducer and any conditioning, “cross talk” can come into play.  Cross talk is the corruption of a signal due to it coming close to a PC or traveling down long cables.  Analog signals are highly sensitive to cross talk and require powerful drives to send them down a signal path efficiently.  Digital signals tolerate cross talk much better and while an analog signal might need +-10 volts to drive it down a path, the same information in digital format would need +-0.5 volts.  

With the advent of inexpensive transducers that can convert analog signals to digital with ease, switching analog signals to digital early on in the system makes sense.  It takes less energy to move the signal through the system and there is much less risk of corrupting the data.  When you consider the fact that the data is directly related to the well being of patients, the more accurate digital format is clearly the best way to go.