Voltage measurement of low current devices

A 15 kOhm resistor is required for voltage measurement if the output of the device is 0.5mA or less.

A device with low current voltage outputs, i.e. with a maximum output current is less than 0.5mA, an additional resistor must be used. Such a device requires a 15 kOhm resistor between the measuring point and the voltage output of the device.
This changes the measuring range of the voltage measurement depending on the measuring card. This guidance applies to AI-8, COMBI-36, SPIDER-40, MULTI-16 and MULTI-24 voltage measurement inputs (AI). Below are instructions for voltage measurement implementation I / O module by type.

Multi-24
Like a normal 0-10V measurement, the measurement type is set to type with 1 function
SetInputTypeF. The resistor limits the voltage seen by Multi24 to 0-3.056V, so
the program must be modified for this measuring range. The most common voltage measurements are read with the function GetVoltageMeasurementF, whose parameters are the minimum and maximum voltage as well as scaled values. With normal 0-10V measurement for minimum and maximum voltage becomes 0 and 10 but when using a 15kOhm resistor at the measuring point the values ​​are 0 and 3,056. If the measured value is not used in the controller for anything other than its transmission to the substation, a correction can also be made in the substation's IEC program. In this case, share the factor by which the value is read from the register at 0.3056.

Multi-16
For existing program profiles, the scaling of the measuring range must be done in the substation
In the IEC program. In this case, the coefficient by which the value is read from the register by 0.3852 is divided.
In new applications, this must be reported at the ordering stage so that it can be taken into account in the controller program profile.

AI-8, COMBI-36 and SPIDER-40
With I / O modules, after series resistance, the voltage range is limited to 0-3.69748V. Scaling of the measuring range can be done in IEC by multiplying the measured reading by a factor of 2.70455 or directly by changing the conversion table so that the 0-10V measuring range corresponds measured in the conversion table 0-36974.8.

Belimo and Siemens actuators have maximum current Imax = 1,0 mA

Fläkt IMS (Airflow Control Unit) Imax = 0,5 mA

Produal Imax = 2,0 mA

Without additional resistance:

Measuring resistors:
Multi24 - 6.6kΩ

Combi36 / AI-8 - 8.8kΩ

U = IR
Rsum = R1 + R2 (= constant)
I is limited to the value of Imax

Additional resistor 15kΩ in series with measuring resistor

The maximum current of the device's Y signal (feedback) should be checked in the data sheet!
When Umax is less than 10,0 V -> the upper part of the measuring range will be cut off.