Rice Lake MSI-9750A CellScale RF Portable Indicator - Manual (Page 11)

MSI CellScale ® System • 9750A User Guide Page 11
MEASUREMENT SYSTEMS INTERNATIONAL
Firmware Version 5-XX for 2450 Modems
SECTION 2 – RF SCALE COMMUNICATIONS
The 9750A is a component 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 refl ected 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 spec-
trum 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
FCC ID: HSW-2450M
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 reason-
able 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 interfer-
ence 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.
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 pseudo-random 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
(0-63) separate networks. The CellScale network uses a ‘Star’ network topology. One unit, usually the CellScale,
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 three products capable of
being the master unit: the CellScale, the 9300 Crane Scale, or the 6260 Trans-Weigh CS Crane Scale. Up to 16
remotes can access the master unit. Current MSI provided remote devices include the 3750CS Indicator, the 9750A
Handheld Indicator, the 9850 Indicator, and the 9020 CellModem. Multiple remotes 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. Each
remote is assigned a specifi c time slot thus guaranteeing data throughput. The CellScale network uses a ‘Star’
network topology. One unit, usually the CellScale, is designated a ‘Master’. The Master transmits a sync pulse on
a regular basis, providing synchronization of all remotes in the designated Network. MSI provides fi ve products
capable of being the master unit: the CellScale, the Smart CellModem 9000 (not 9020), the MSI-9260 ruggedized
Crane Scale, the MSI-9300 Porta-Weigh+ Crane Scale (with local display), or the MSI-6260CS Trans-Weigh CS
Crane Scale. Up to 15 slaves can access the master unit. The 9750A is always a ‘Slave’. Multiple 9750A units
can coexist on one network, or can be easily switched to other networks as required.
For more on setting up CellScale networks, please refer to the MSI-9000 CellScale User Guide.
ANTENNA
The 9750A uses a built in “Patch” antenna with no external visible element. The patch is located in the end of the
9750A above the display. In most installed CellScale networks, the patch antenna is essentially omnidirectional.
However, in systems where the 9750A is reaching the limits of transmission range, the 9750A will achieve better
range by pointing it toward the master CellScale’s antenna.