Mantracourt Electronics Limited
DCell & DSC MantraCAN User Manual
66
Key Requirements
•
The main bus cable must be terminated at either end
•
Where the bus does not go directly to each attached device, each ‘stub’ cable connecting to the bus should have
just one device on it
•
Stub branches should be kept as short as possible
•
Stubs are not terminated
Bus Layout and Termination
The ideal bus is a single length of cable, terminated at either end. Each end connects to a communicating device;
while other devices are connected as near as possible directly to the main bus as it passes them (i.e. not on long
side-branches).
The bus must be terminated at both ends to avoid reflections. Connecting a 120 Ohm resistor between the CANH
and CANL lines does this.
Loading
It is important that the bus is loaded at each end with the corresponding line impedance, this is normally 120Ohm
Strain Gauge Sensitivity Adjustment (DSC ONLY)
For DCell strain gauge sensitivity adjustment please consult factory.
If your strain gauge does not deliver a 2.5mV/V full scale output, you may want to adjust the sensitivity of the
electronics (hardware) and/or the software gain controls.
If you want to test with an input of
more
than 2.5mV/V, you will have to adjust the hardware sensitivity to avoid
saturating the input. If it is less, you can correct in software alone, but increasing sensitivity will generally improve
accuracy.
To adjust the mV/V for DSC, an extra resistor ‘Rg’ is fitted across the pads RG, as shown above, in
Identifying the DSC ‘Rg’ Resistor
Identifying Sensor End Connections
The link across TC can be cut to disconnect the internal 100R gain resistor: This is needed for lowering the
sensitivity.
The resistor is 0805 size surface mount chip.
A 0.1%, 5ppm/Deg C resistor for the high stability version & 25ppm/ Deg C for the Industrial must be used to
maintain performance.
Reducing Sensitivity
To accommodate a maximum sensor output
larger
than 2.5mV/V, it is necessary to reduce the electrical sensitivity
of the input circuitry.
To decrease sensitivity, the link
TC
is cut, and the value of the resistor fitted, in
Ω
, should be –
R
g
= (required mV/V) x 40
Example: For 10mV/V
R
g
= 10 x 40 = 400
Ω
TC
RG
