Wilcoxon Sensing Technologies
an Amphenol Company
Frederick, MD 21701 USA Page 7 of 23
Tel: +1 (301) 330-8811
Tel: +1 800 WILCOXON
Fax: +1 (301) 330-8873
www.wilcoxon.com
7Ordering procedure and options
7.1 Step 1 - Input type
Specify the type of sensor to be connected to the
transmitter, either an accelerometer or a velocity transducer.
7.2 Step 2 - Sensitivity
Specify the sensitivity of the sensor. Units are mV/g for
acceleration and mV/ips for velocity.
7.3 Step 3 - Detector type
Next, specify the desired detector type. Four types of power
detectors are available.
*True peak detector option available for input/output type “A”
only.
The properties and behavior of each type of detector are
explained in the following sections.
7.3.1 RMS
An RMS power detector operates on frequency domain (FFT)
data. It computes the true RMS power level of the input
signal by summing the power levels of all FFT bins in the
measurement bandwidth. Due to averaging, an RMS
detector is relatively insensitive to brief spikes of vibration
and other transients and tends to smooth the signal
response.
True RMS detection is a very accurate method of
determining the total power contained in a signal. It is used
in vibration detection where it is desired to know the total
amount of true vibration energy exhibited by a machine.
The digital signal processor always calculates the true RMS
power level of the input signal and derives peak and peak-to-
peak values from the RMS value.
7.3.2 Peak (“equivalent”)
Peak detection can be selected when it is desired to know
the peak value of the vibration. The peak value is calculated
by multiplying the detected RMS power level by . This
method of conversion results in an “equivalent” peak power
value of the input signal. It is accurate only when the input
signal consists of a pure sinusoidal waveform. Since, in most
cases, the vibration energy is primarily due to a single, high-
level sinusoidal vibration, this method of peak detection
works well.
Many vibration transmitters develop a peak value for
vibration by using this method. The iT150 Series transmitters
have this detection method available to provide comparable
results to other vibration transmitters in use. It is also useful
where users simply wish to have the signal output be in
terms of peak vibration rather than RMS.
7.3.3 Peak-to-peak (“equivalent”)
Peak-to-peak is simply two times the equivalent peak value.
It is best used for displacement measurements. Select this
detector option when plant maintenance records are in
peak-to-peak units.
Tech tip! The choice of RMS versus equivalent peak
detection is usually a matter of user preference. Both work
from the same basic detection method. The choice is usually
determined by local convention. Additionally, historical
vibration data may be in terms of either RMS or peak
vibration, and therefore the selection of vibration units can
be in line with the plant’s historical data.
7.3.4 True peak (Input/output type = “A”only)
Overview
The iT150 also offers a “True Peak” detector option. In
contrast to an RMS power detector, which operates on the
band-limited frequency domain data, the true peak detector
operates on full bandwidth (10 Hz to 25 kHz) time domain
waveform data. By operating on the raw data from the
analog-to-digital converter, the true peak detector accurately
responds to short-duration transients and impulses.
True peak detection is beneficial where it is desirable to
capture short transient vibration events or where non-
sinusoidal waveforms would cause large errors in an
equivalent peak calculation, due to the presence of high
frequency energy in the waveform. Some common
mechanical causes of this type of energy are early bearing
