CellScale
®
System • 3750CS-5 User Guide Page 7
MEASUREMENT SYSTEMS INTERNATIONAL
Software V2-21 or greater, 2nd Generation Modem
SECTION 2 – RF SCALE COMMUNICATIONS
INTRODUCTION – THE CELLSCALE SYSTEM
The 3750CS is an element of the MSI CellScale System. The CellScale system uses frequency hopping spread-
spectrum RF Modem technology transmitting in the 2.4 GHz ISM band.
RF Modems have been problematic as the RF bands are very hostile, corrupted by noise, path loss and inter-
fering transmission from other radios. Even in a pure interference-free environment, radio performance faces
serious degradation through a phenomenon known as multipath fading, a problem particularly prevalent for
indoor installations. Multipath fading results when two or more reflected rays of the transmitted signal arrive
at the receiving antenna with opposing phase, thereby partially or completely cancelling the desired signal.
Spread spectrum reduces the vulnerability of a radio system to both interference from jammers and multipath
fading by distributing the transmitted signal over a larger region of the frequency band than would otherwise
be necessary to send the information. This allows the signal to be reconstructed even though part of it may be
lost or corrupted in transit.
Spectrum has been set aside at 2.4 GHz in most countries for the purpose of allowing compliant spread spectrum
systems to operate freely without the requirement of a site license. In the USA, there are absolutely no site
licensing requirements. The CellScale system is also programmable for use in most European countries. Please
contact MSI for worldwide compliance information.
FCC STATEMENT
Note: This unit has been tested and found to comply with the limits for a Class A digital device, pursuant to part
15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference
when the equipment is operated in a commercial environment. This equipment generates, uses, and can radiate
radio frequency energy and, if not installed and used in accordance with the instruction manual, may cause
harmful interference to radio communications. Operation of this equipment in a residential area is likely to cause
harmful interference in which case the user will be required to correct the interference at their expense.
The Transmitter Module is licensed as FCC ID: HSW-2450M.
NETWORK DESCRIPTION
The CellScale system uses frequency hopping which is produced by transmitting the data signal as usual, but
varying the carrier frequency rapidly according to a pseudorandom pattern over a broad range of channels, in
this case 86 discreet frequencies. These 86 frequencies are combined in different “hopping patterns” to provide
64 separate networks.
The CellScale network uses a ‘Star’ network topology. One unit, usually the scale, is designated a ‘Master’.
The Master transmits a sync pulse on a regular basis, providing synchronization of all remotes in the designated
Network. Thus it forms the center of a cell. MSI provides four products capable of being the master unit: the
CellScale, the CellModem, the 9300 Porta-Weigh+ Crane Scale, or the Trans-Weigh 6260CS Crane Scale. Up
to 16 slaves can access the master unit. The 3750CS is always a ‘Remote’. Multiple 3750CS units can coexist
on one network, or can be easily switched to other networks as required.
The CellScale system uses TDMA (Time Division Multiple access) to arbitrate between multiple remotes. TDMA
is slotted or scheduled.. Each remote has an assigned time to transmit and always is alloted time. TDMA assures
a consistant throughput from each remote.
For more on setting up CellScale networks, please refer to the CellScale manual,