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Active interface converters

Active interface converters provide maximum flexibility for the application by the use of an external control supply voltage. Configuration with active interface converters is extremely easy because input and output resistances and voltage drops are compensated by the auxiliary supply. They support electrical separation as well as conversion from one signal type to another or reinforcement. The load of the measured value transmitter is negligible.

Passive interface converters

Passive interface converters do not require an external control supply voltage. This advantage can only be used by current signals that are converted 1:1. Reinforcement or conversion is not possible. The converters are used for complete electrical separation of current signals and to protect the inputs and outputs. Passive interface converters do not operate reaction-free, i.e. any load on the output produces an equal load on the input signal. When the passive converter is to be used, the output power of the sensor and the input resistance of the analog input must be analyzed.

Calculation guide for passive converters

Important: please note the following when using passive interface converters:

When the output is open, the input becomes high impedance, and the current-driving voltage of the measuring transducer U_E must be sufficient to drive the maximum current of 20 mA over the passive converters with a voltage loss of U_V = 2.8 V and the load R_B.

This means:

U_B ≥ U_E = 2.8 V + 20 mA x R_B

Distribution of the voltages in the case of passive interface converters

The following figure shows the input voltage U_E as a function of the load R_B taking into account the voltage loss U_V. If the load is known, the y-axis shows the minimum voltage that has to be supplied by the current source in order to drive the maximum current of 20 mA over the passive interface converter and load.

Input voltage depending on the load at I_a = 20 mA

Load rating of the outputs

A maximum output load is specified for current signals. This resistance value specifies how large the input resistance of the next device connected in series can be as a result of the power of the converter.

For voltage signals, the maximum current that can be drawn from the output is the decisive factor.

2-way separation

In the case of 2-way separation, the input is electrically separated from the output. The "zero potential" of the control supply voltage is the same as the reference potential for the analog output signal.

2-way separation

3-way separation

For the 3-way separation, each circuit is electrically separated from the other circuits, i.e. input, output, and control supply voltage do not have equipotential bonding.

3-way separation

Dimensions

Dimensions for 3-way separated analog converter with width 6.2 mm