Stacked Signal Conditioning Input Wiring

To facilitate the universal conditioning on a single connector the Dragonfly uses an 8-pin Fischer connector for analogue signal input. Individual conditioning types are configured through a combination of wiring and the HGL Acquisition software.

Table 1 - Dragonfly 8-pin Fischer Pin Assignment


A number of different sensor wiring configurations are possible with this connector, these are listed below. Wiring Diagrams for each connection type are also provided. 

  • AC Voltage (BNC terminated cable provided)/Dynamic Strain
  • DC Voltage 
  • AC & DC Voltage
  • 1/4 Bridge Strain
  • 1/2 Bridge Strain
  • Full Bridge Strain
  • IEPE (ICP)

1/4 Bridge Strain (3-wire method)

The 3 wire method of wiring or ¼ bridge provides better balance and noise performance than the more traditional 2-wire method (see below).

The measurement bridge can be either as shown or swapped (gauge and Completion resistor changed around).

In the configuration shown the internal (55kOhms) shunt cal resistor is actually shunting the completion resistor. Whilst this does not affect the value of the calibration the sign of it is affected and so individual customers need to determine which way round the gauge and completion should be to match their own conventions.

It should be noted that there is the capability to modify the internal shunt resistor by wiring an additional resistor externally as shown in the diagram below. Note this resistor is in parallel with the internal shunt resistor.

Also note the link between pins 2 & 6, this is required to connect the mid-point of the internal half bridge completion to the amplifier.

Figure 13 - Three Wire 1/4 Bridge Wiring

1/4 Bridge Strain (2-wire method)

The 2 wire method of wiring or ¼ bridge provides worse balance and noise performance than the 3-wire method described above. However if the strain gauge is close to the Dragonfly then it does provide an easier wiring method for similar performance. For long distances between the gauge and the Dragonfly the 3 wire method is highly recommended.

The measurement bridge can be either as shown or swapped (gauge and Completion resistor changed around).

In the configuration shown the internal (55kOhms) shunt cal resistor is actually shunting the completion resistor. Whilst this does not affect the value of the calibration the sign of it is affected and so individual customers need to determine which way round the gauge and completion should be to match their own conventions.

It should be noted that there is the capability to modify the internal shunt resistor by wiring an additional resistor externally as shown in the diagram below. Note this resistor is in parallel with the internal shunt resistor.

Also note the link between pins 2 & 6, this is required to connect the mid-point of the internal half bridge completion to the amplifier.

Figure 14 - 2 Wire 1/4 Bridge Wiring

1/2 Bridge Strain

In the configuration shown the internal (55kOhms) shunt cal resistor only operates on gauge 1.

It should be noted that there is the capability to modify the internal shunt resistor by wiring an additional resistor externally as shown in the diagram below. Note this resistor is in parallel with the internal shunt resistor.

Also note the link between pins 2 & 6, this is required to connect the mid-point of the internal half bridge completion to the amplifier.

Figure 15 - 1/2 Bridge Wiring

Full Bridge Strain

Full bridge strain only utilizes the power and amplifier inputs of the Dragonfly. The shunt can still be used but only operates on gauge 1.

It should be noted that there is the capability to modify the internal shunt resistor by wiring an additional resistor externally as shown in the diagram below. Note this resistor is in parallel with the internal shunt resistor.

Also note the link between pins 2 & 6, is not needed in this configuration as the internal half bridge is not in use.

Figure 16 - Full Bridge Wiring

Dynamic Strain

Dynamic strain provides an AC only signal from a single strain gauge. The gauge is energized by an internal constant current generator which is fully programmable.

For situations where the dc component of strain is not required this configuration provides a much simpler wiring model than a bridge configuration. It is also simpler to use operationally. 

Figure 17 - Dynamic Strain Wiring

Voltage Measurements

Voltage measurements on the stacked system can be wired up in one of three different ways depending on whether AC, DC or both are required.

HGL supplies AC Voltage / IEPE cables for each channel with the Dragonfly, the wiring of this is shown below.

Figure 18 - AC Voltage / IEPE Wiring

DC voltage can be measured through the DC bridge board very simply as indicated below. With the standard cables supplied by HGL with the Dragonfly this configuration does need wiring with the bare end cables.

Using a similar concept AC and DC voltage can be achieved through wiring and software control using the wiring scheme in Figure 20. Once again the bare end standard cable would be needed for this.

HGL can also provide pre-wired cables for the DC or AC/DC Voltage configurations.

Figure 19 - DC Voltage Wiring

Figure 20 - AC/DC Voltage Wiring