Analog inputs

Analog input applications

You can use an analog input to monitor an analog signal, for example a flowmeter, to monitor how much water flows through a pipe.

For analog input operation, your meter takes an analog input signal and provides the resulting scaled value.

Your meter’s analog I/O option modules can measure either low voltage or current using standard analog transducers such as 4–20 mA current transducers.

Analog input voltage and current mode

You can set the analog input’s mode for voltage or current sensing.

In current mode, the analog inputs have a low input resistance while the meter is powered on, and a high input resistance when the meter is powered off. In voltage mode, the analog inputs have a high input resistance regardless of whether the meter is powered or not.

Note: When unpowered, your meter’s analog inputs act like they are in voltage mode (high input resistance).

When connected to a current output transducer, this high resistance can create a high voltage. Standard (i.e., 4–20 mA) current transducers have open circuit protection and can handle a high input resistance; however, if non-standard transducers are used high voltages may be generated. Your meter’s analog input has circuitry to limit this voltage, but it may not be sufficient with a very high-power current source.

notice

EQUIPMENT DAMAGE

Ensure the analog input is configured for the correct voltage or current mode before connecting or activating the current transducer.
Do not exceed the device’s ratings for maximum limits.

Failure to follow these instructions will result in equipment damage.

Analog input behavior

Analog inputs may show a value below zero scale if an open circuit is detected on the input port.

Analog input zero scale and full scale values

In most cases the output range of the sensor feeding the analog input matches the hardware limits of your meter’s analog input port. In that case, the analog input’s zero scale and full scale values are the same as the sensor’s represented range. For example:

Analog sensor	Meter’s analog input signal	Analog input register values
0–50 psi represented by a 4–20 mA signal	4–20 mA analog input range Input value: 12 mA	Full scale = 50 (psi) Zero scale = 0 (psi) Scaled value: 25 (psi)
0–50 psi represented by a 0–20 mA signal	0–20 mA analog input range¹ Input value: 12 mA	Full scale = 50 (psi) Zero scale = 0 (psi) Scaled value: 30 (psi)

Analog sensor

Meter’s analog input signal

Analog input register values

0–50 psi represented by a

4–20 mA signal

4–20 mA analog input range

Input value: 12 mA

Full scale = 50 (psi)

Zero scale = 0 (psi)

Scaled value: 25 (psi)

0–50 psi represented by a

0–20 mA signal

0–20 mA analog input range¹

Input value: 12 mA

Full scale = 50 (psi)

Zero scale = 0 (psi)

Scaled value: 30 (psi)

¹ Analog I/O option module must have firmware version v1.2 or later.

If the sensor’s output range does not match your meter’s hardware limits, you must calculate the full scale and/or zero scale values by analyzing the system.

For more information see Analog Input Module in ION Reference help.