M1500 User Guide Section 1
© 2002 Micro Movements Ltd Ver. 2.0 Page: 3
1.1.4. Filtering
It is often required in measurement systems, to provide noise filters. In digitising systems, anti-aliasing
filters are often required. The M1500 Signal Conditioners have the facility for built-in filters that can be
switched in or out under RS232 control.
1.1.5. Multiplexing
The M1500 system can be fitted with a multistage multiplexing card enabling up to 16 analog
channels to be multiplexed onto a single analog input of an ADC. Thus using a typical 16 channel
ADC it is possible for the M1500 system to multiplex up to 256 analog channels into a single ADC.
This can be configured as a 64 channel system (one M1500 housing), a 128 channel system (two
M1500 housings) or a 256 channel system (four M1500 housings) by simple jumper selection.
1.1.6. Analog to Digital Converter (ADC)
The analog output, typically up to ± 10 volts, from a signal conditioner channel is converted to a
digital value by an ADC in the host computer. ADC’s for this type of application will typically be
16 channel and may be 12, 14 or 16 bit resolution for ISA or PCI configuration. The M1500
multiplexing card utilises the multiplex control outputs from an ADC to operate its internal
multiplexing, ensuring signal efficacy and compatibility with a large number of different
manufacturers’ products. The M1500 is physically configured for direct connection to the MicroStar
range of intelligent ADC’s. Connection to other manufacturers devices can be implemented easily.
For advice on suitable ADC’s the Micro Movements Application Support will be happy to assist
and Micro Movements can supply appropriate cables for instant connection to most available ADC’s.
1.1.7. High Speed Applications
The multiplexing of up to 256 channels into a single ADC by the M1500 system allows for space
efficient, cost effective implementation of high channel count applications. However, there are
technological limitations on the speed at which the signals can be multiplexed. Finite switching
times, settling times and digital transition delays exist in even the fastest available semiconductor
devices. This places a limitation of 1MHz maximum throughput rate on any multiplexed system whilst
retaining the accuracy of measurement. This means that for a system with 256 channels, sampling rates of
just under 4KHz on each channel are possible. With reduced numbers of channels (with ADC’s that
support equal mode multiplexing) the individual channel sampling rates can be increased.
Max. channel sampling rate = 1000 K samples per sec.
number of system channels
For ADC’s that only operate in burst mode then that is the maximum throughput rate and the maximum
channel sampling rate is: burst rate/256 samples per sec.
It is obvious from the above that in order to obtain higher individual channel sample rates it is necessary to
use more ADC’s. The M1500 system can be configured for Direct Output. In this instance the multiplexers
are bypassed so that individual signal conditioning channels are accessible in permanent real time. The
speed at which channels can be sampled is then only limited by the ADC performance. (See also Section
1.2.3.)
