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If required, the entire unit can be embedded in a potting compound: A two-part epoxy compound can be used, but
bubbles and gaps must be avoided to prevent mechanical stresses which could break the device.
The compound used must be specified for electrical use, and have sufficient thermal conductivity to cope with the
heat given off (up to 1W on a 15V supply).
DSC no additional electrical shielding is required, but moisture and/or mechanical protection are often required.
Any simple box or enclosure can be used. If metal, the enclosure should be grounded to the SH connection (see
Communications Cabling and Grounding Requirements below).
Soldering Methods
Take care soldering cables to the pads. Use a temperature controlled soldering iron set to a maximum 330ºC, for no
longer than 2 seconds per pad. Excessive heat or increased soldering time may result in damage to the PCB.
NOTES:
1. Solder with water-soluble flux should not be used (even low-residue), as this can leave a surface film which
attracts atmospheric moisture, degrading measurement performance.
2. DCell units can be damaged by poor soldering, due to the small nature of the circuit boards: Overheating or
applying any pressure to a pad can de solder components on the other side of the board, or cause the pad itself
to become detached.
Power Supply Requirements
The power supply needed is nominally 5.6 to 18V DC, but any possible droop or ripple must be included: The
devices contain 'brown-out' detection, which may trigger if the supply voltage at the device drops below the 5.6
volts.
A single device consumes typically 40mA with a 350Ω gauge connected (except RS232-output units, which use about
10mA more).
An installation should therefore assume at least 60mA per unit, and allow for extra current being taken at power-on
(though supply voltage can safely drop temporarily), and for possible voltage drops in long cables.
Any power-supply ripple should be below 100mV, and supply arrangements should provide current limiting for fault
conditions (see Electrical Protection, above).
Cable Requirements
Strain Gauge Input (DSC)
For optimal performance twin twisted pair with individual shields is recommended, this gives good noise immunity.
Maximum length should not exceed 20m. Normal 4 core shielded cable can be used in areas of low electromagnetic
noise.
Power and Communication
Again, twin twisted pair cable is recommended for this. The cable should have the following characteristics.
• Twisted-pair with independent shields
• Characteristic impedance 50-150 ohms
• Core to core and core to shield capacitance below 300pF/m
A suitable type is BICC Brand-Rex BE56723 (also equivalent to Belden type 8723).
In the UK, this is available from Farnell, part number 118-2117
Normal 4 core shielded cable can be used in areas of low electromagnetic noise.
For RS232 operating at high baud rate on longer distances a triple twisted pair cable is recommended. A suitable
type is BICC Brand-Rex PD3003 (also equivalent to Belden type 8777).
In the UK, this is available from Farnell (enter 'Belden 8777' for real length options).
Micron Meters DCell & DSC User Manual
58
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