For the wireless transmission of several information channels such as ones that may be produced by strain gages on a rotating shaft, several different RF transmission frequencies are necessary.
This normally would require a RF receiver for each of the different frequencies resulting in a significant increase in cost.
Multi-channel telemetry systems such as the Modular Telemetry Pro (MTP) produced by KMT Telemetry interlace and bundle the different channels time wise with each other until they are available as a "2-wire line" to be transferred with one single RF transmitter.
This type of transmission is realised by digitising, multiplexing and PCM (Pulse-Code-Modulation) encoding of all signal channels. This kind of digital PCM transmission has been used for many years in communications technology.
This technology has advanced wireless telemetry systems to the point where these instruments can gather data in the harshest of conditions. The wireless telemetry systems produced by KMT is a great example of this.
The KMT Telemetry R16 PCM Rotate, for example, is an axial unit for collecting dynamic measurements from rotating devices under shock and vibration loads such as railway wheels, gear boxes and test rigs. It enables conditioning, digitisation and wireless transmission of up to 16 strain gage signals. The fully sealed housing and extended operating temperature range make it particularly suitable for off-road and testing in arduous conditions.
The advantages of PCM transmission are:
- Constant signal/noise ratio by digitisation of the signal
- Multiple use of one transmission-channel by multiplexing
- Interference free signal transmission, low susceptibility to crosstalk
- Direct acquisition and processing of the received digital PCM signal to a PC