LORD V-Link-200, Руководство пользователя

Страница: 50 / 102

V-Link
®
-200
User Manual
6.8.1 Measuring Small Currents (4 to 20mA Sensors)
LORD Sensing nodes with analog inputs, such as theV-Link-200 and , support a wide range analog
sensors including acceleration, vibration, strain, load cells, torque, pressure, magnetic fields,
displacement, geophones, and more. To support these sensors, the nodes measure small voltage.
Additionally, sensors with small current outputs, such as 4 to 20mA sensors, can be used with the
nodes by adding a precision sampling resistor across a single-ended input channel to the node. An
example circuit is shown in Figure 39 - Small Current Measurements .
l
Node Channel and Sensor Output Range: Either the single- channel or
differential analog input channel can be used to measure current. The external
circuit and node settings are different for each. The single-ended option is simpler
allows less adjustment. For applications in which very small currents will be
measured, the differential inputs offer better noise immunity and programmable
gain settings. Available gain settings vary between node models. Differential inputs
can be factory configured for various bridge completion and impedance values. For
this application, the standard full- bridge configuration is assumed. For other
configurations contact LORD Sensing Technical Support.
l
Power Source: If the sensor will be operating continuously in the 20mA range, or if
multiple analogs inputs are in use, it is recommended that an external source be
used to power the sensor or the node. Typically nodes can only supply 50mA (to all
sensors), so 20mA would be a significant portion of the node capacity and would
drain the internal battery quickly. However for applications with lower current
requirements and measurement ranges, the internal battery may be a better option
to mitigate potential noise sources, especially when using differential channels.
50