Instructions

UM-0085-B09 DT80 Range User Manual Page 313
RG
• a precision 5.00V supply. In this case the DT80 does not measure Vex – it assumes that it is exactly 5.00V. The
power supply should be located close to the bridge to avoid voltage drop due to cable resistance.
.
Figure 140: Wiring for 6-wire bridge using external voltage excitation
To measure
Use the command
bridge output (3V supply)
1*V(BR,W) 1BGV(N)
bridge output (6V supply)
1+V(2,BR,W) 1BGV(N)
bridge output (5.00V supply)
1BGV(N)
Assuming a non-precision power supply, two channel definitions will be required.
• The first (
1*V) measures the voltage between the * and # terminals, and includes the BR (bridge reference)
option which indicates that its value is to be used as the excitation voltage for subsequent bridge channels in
the same schedule. It is also usually made a working channel (
W) because it is merely an intermediate
measurement.
If a 3-6V supply is used then the appropriate channel definition would instead be
1+V(2,BR,W): measure
between + and #, scale by 2 then use as bridge reference.
If a 5.00V precision supply is used then this channel is not required.
• The second (
1BGV) measures the bridge output voltage between the + and – terminals. The N (no excitation)
channel option is specified because in this configuration the excitation is provided externally.
B2 – 4-Wire BGV Inputs
Note: Using the HV channel type to measure the bridge excitation voltage is not recommended. This channel type is normally not
sufficiently accurate for bridge applications.
This configuration is similar to the 6-wire configuration except that the bridge excitation is supplied by the DT80's internal
voltage source (approx 4.5V). This supply is in the range 3-6V, so it requires that the excitation be measured using the +
rather than the * terminal then scaled by 2.
Series 4 models also provides built-in 16-bit DAC converter at V/I DAC terminal. It capable to supply ouput voltages up to
10V, it also can be used as an external excitation power source Vex.
Note also that the V channel option must be specified to tell the DT80 to switch on voltage excitation while the voltage
measurement is being taken. This option is the default for the BGV channel, so it need not be specified.
This configuration is not recommended if the lead lengths are long, because the return wire is carrying the excitation
current and we cannot compensate for the voltage drop over the length of the return wire. This will lead to an inaccurate
excitation voltage measurement, and hence an inaccurate bridge measurement.
Figure 141: Wiring for 4 wire bridge input using internal excitation
To measure
Use the command
bridge output
1+V(BR,2,V,W) 1BGV