Instructions

UM-0085-B09 DT80 Range User Manual Page 24

In a shared-terminal configuration, a sensor’s "return" or "negative" wire is usually connected to the channel's # terminal.

The remaining sensor wire (the "positive" or "signal") is connected to any of the channel’s other three terminals. The

common terminal need not be at ground potential – all voltage measurements (shared or unshared) are differential, i.e.

only the difference

in voltage between the two terminals is reported.

For shared-terminal inputs, the channel number is given a suffix indicating the terminal to which the positive wire is

connected. For example, a shared-terminal voltage input applied to channel 1 between the + and # terminals is

recognized by the channel definition

1+V.



Independent Analog Inputs

An independent input (also known as an "unshared" input) is one that connects to its own terminals and does not share

any of those terminals with any other inputs. For example, in Figure 5, sensor A is connected to channel 1’s + and –

terminals, and sensor B is connected to the other two terminals of the channel. In other words, each sensor’s terminals

are independent of the other’s — no terminal is used by both sensors.

Figure 5: Wiring one or two independent inputs to a single channel (voltage inputs used as example)

Note: each analog input channel can support two independent voltage inputs. In the above example, the channel definition

1V will read

sensor A while

1*V will read sensor B. The channel definition syntax is fully described in Channels (P33).

Sensor Excitation

Many sensors require excitation (electrical energy) so that they can provide an output signal. For example, to read the

temperature of a thermistor, excitation current is passed through the thermistor to generate a voltage drop that can be

measured.

The DT80 can provide:

• Voltage source of approx. 4.5V via 1kΩ. Useful for powering some sensors however the supply is not regulated

and consequently liable to drift with temperature

• 2μA (approx.) current source. Excitation for high resistance measurement. Very stable over environmental

temperature range.

• 200μA (approx.) current source. Default excitation for resistance measurement. Very stable over environmental

temperature range.

• 2.5mA (approx.) current source. Default excitation for RTD and bridge measurement. Very stable over

environmental temperature range.

• DT 80 Series 4 provide 16-bit resolution Voltage/Current digital-to-analog converter outputs at V/I DAC terminal.

The current outputs can be set within 0-24mA range and voltage is within 10mV-10V range. The DAC output

can also be used as an external voltage or current excitation for many sensors. It can also be externally routed

to EXT* terminal.

• User supplied external excitation EXT* terminal. The user can provide an external excitation which is

appropriate to the sensor being used. See the Excitation category in the DT80 Channel Options (Table 5: DT80

Channel Options – P47).

More Information

For full details on how to connect sensors and make measurements using the DT80's analog inputs, see Analog

Channels (P302).