Current - dataTaker DT80 User Manual

Current

Current (rate of electrical charge movement) is measured by inserting a known shunt resistance into the circuit, and
measuring the voltage across it. Using Ohm's Law, Current = Voltage / Resistance.
The I channel type returns the current value in milliamps (mA).
The DT80 incorporates an internal 100Ω shunt resistor between the # terminal and analog ground. Alternatively, an
external shunt may be used. The value of the external shunt must be known and must be specified when the channel is
defined.
For example, the channel definition
the internal shunt, and returns via the AGND/EXT# terminal.
2+I(51.2)
On the other hand,
terminals of channel 2.
Channel Options
The following channel options are commonly used when measuring currents:
A
• (attenuator) specifies that the DT80's input attenuator should be enabled, which allows voltages of up to 30V
(up to 50V in Series 4) to be measured across the shunt resistors. Note that this option is not available if the
internal shunt is used.
• the excitation options specify how the current source is powered:
V
(enable internal 4.5V voltage source on * terminal) or
terminal).
E
• (external excitation) specifies that the power supply for the current sources is connected to the DT80's EXT*
terminal. This will then be automatically connected to each current source for the duration of a measurement,
and then disconnected.
MD
• (measurement delay) specifies that the DT80 should wait n ms (default 10ms) after selecting a channel
n
before starting the actual measurement. This can be useful in conjunction with the E option, as it allows the
sensor some time to stabilise after power is applied to it.
• the channel factor specifies the shunt resistance in ohms (default 100.0 Ω)
GL ES
• n, as for voltage measurements
x,
The following sections describe some common wiring configurations for measuring current.
C1 – Shared Terminal Current Inputs using External Shunts
In this configuration up to three separate current sources can be measured. This is done by measuring the voltages
across the shunts in the shared terminal configuration; see
To avoid cross-channel coupling, connect the bottom of the shunts with the minimum of shared resistance to the sense
point.
The resistance of each shunt should be specified as the channel factor.
UM-0085-B09
RG
3#I
will measure the current which enters at channel 3's # terminal, flows through
will return the current flowing through a 51.2Ω shunt wired between the + and #
Figure 128: Wiring for shared-terminal current input using external shunt
To measure
I1
I2
I3
DT80 Range User Manual
N
(assume external power supply; default),
E
(assume external supply connected to EXT*
V1 – Shared Terminal Voltage
Use the command
1*I(R1)
1+I(R2)
1-I(R3)
Inputs(P305).
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