When choosing an analog measurement transducer for a variety of instrumentation monitoring applications including machine monitoring, quality assurance, and more, you will be given a choice of signal types.
The most common signals for these transducers are either voltage (0-5 volts DC, or 0-10 volts DC) or current (generally 4-20 milliamps). Both types are low-cost and easy to find, and both have advantages and disadvantages depending on the environment in which they are being used.
Applications Specialists at CAS DataLoggers explore both the pros and cons of these two analog signals.
DC Voltage (0-5v, 0-10V) DC voltage is a very basic analog signal which gives you excellent resolution, is easy to connect and troubleshoot, and is well suited to lab environments. The sensors which use a voltage output tend to be quick and easy to connect. They require an input excitation voltage and have an easy to identify output wire carrying the measured signal.
However, a voltage signal is not a good fit if you are planning on using it in an industrial environment. Even when using shielded wire, the signal is highly susceptible to interference from high voltage AC, motors, pumps, relays, etc. The signal is also susceptible to voltage drops on log runs of signal wire.
DC Current (4-20mA) In contrast, a DC current loop offers several advantages in industrial settings. This signal is not as susceptible to electrical interference from high voltage AC, motors, pumps, or relays, nor is it susceptible to signal loss due to the length of the wiring run (voltage drop). A 4-20mA loop can also power multiple devices using one excitation source and requires much fewer wires. Additionally, a 4-20 mA signal offers fairly easy fault detection because its Ď0í point is at 4mA, so if a negative reading is shown in the scaled readings, thereís likely a problem with the signal.
However, a 4-20mA signal will not give you the same resolution as a voltage signal so it is not necessarily recommended for use in a lab environment. Another drawback of a 4-20mA signal is that you will generally require shunt resistors to take a reading on most data logging equipment.
While there are many other considerations to take into account when choosing a transducer, environment and signal distance should be your main factors.
This outline will hopefully have given you a good basis for the best signal choice between voltage and current.
A few years ago, I was working on the design of a data acquisition system (DAS) that would eventually need to be tested when manufactured. It had both high-side current sensing and floating diff-amp input channels. I could either recommend to the client that some expensive equipment be bought and configured for such testing or else design and build some prototypes of a Floating Differential Source (FDS) which would cost much less. I did the latter.
As an engineer, eventually you will have to insert an equation into your written work or presentation. This can be a struggle as equation editors are not always the friendliest. However, there is good news. The equation editor in Word has improved immensely (I am using version 2010 here). In this blog we look at how to insert an equation into a Word document. As a bonus, there is information on how to insert an equation into a web page with an html code generator website.
Wait a minute. Letís see if I understand this. (Here Iím channeling you, the puzzled reader, after youíve grabbed me in the coffee break of a Filter Wizard lecture morning). The frequency of the nth harmonic of a sinusoid is n times that of the fundamental. The nth harmonic distortion is defined as the ratio of the amplitude of the nth harmonic to the amplitude of the fundamental. So the 1st harmonic distortion isÖ the ratio of the amplitude of the fundamental to the amplitude of the fundamental and thatísÖ unity. I. Do. Not. Understand.