High voltage measurement is easily & safely accomplished; when isolation amplifiers are combined with voltage dividers, to fit the measurement span of the connected data converter. 

An example of this is shown by considering; a conversion of, the supply power to a dc motor. When measured using voltage dividers alone; the possibility is always present, that improper grounding can result in equipment damage. The addition of isolation amplifiers to the plan, provides hundreds of volts of protection to the system, & the added benefit of ground loop elimination. 

When is this important? While high high voltage protection is not necessary in all measurement applications, some applications see the need after damage is done; isolation amplifiers protect the sensing equipment in those applications that need it, allowing an application to meet requirements with a added level of protection.

The ROI-USB combined with the ROI-ISOV is an improved way to isolate your reading of high voltage. Input to output (2-way) 1.5Kv isolation. Fast response. True analog signal conditioning.

a voltage divider can expand an isolation amplifier range

In applications where higher voltages than the ROI-USB5 A-D can read need to be monitored, the ROI-ISOV10 can be used to couple a voltage divider; using an isolation amplifier, to monitor high voltage with the 5V voltage A-D.

The voltage divider can consist of 2 resistors, with values that represent the fraction of the applied voltage, the divider needs to produce. In general the calculation that the divider follows, is;

Rt = Vin/Imax

where Imax is the maximum desired current into the divider (not the maximum available, e.g.: 1mA). 

Rt = (R1 + R2)

knowing that; the choice of R1 & R2 is dependent on commercially available values, or the use of potentiometers (keeping the input voltage a little below the A-D max can give more options). 

Vout = (Vin X R1)/(R1 + R2)

Vout is actually the voltage fed into the measuring system.

An example of an application where this could be used is a 24Vdc level monitor. The use of sensor transmitters in a monitoring system, depends on having a power source that meets minimum requirements. While sensor transmitters have a wide acceptable voltage range, the internal A-D shunt resistor only has the remaining voltage of the supply after subtracting the transmitter and line voltage drop. 

Where could this be helpful? If the supply powering a transmitter network developed a problem and produced lower voltage than the design level; it is possible that the transmitter output could be artificially low, if the measurement was at the upper end with an incorrect supply voltage. This measurement could be used to alert an operator to the situation before it became a problem.

The ROI-USB combined with the ROI-ISOV10 is an improved way to isolate your reading of high voltage. Input to output (2-way) 1.5Kv isolation. Fast response. True analog signal conditioning.

Learn more about ROI-USB general purpose A-D’s, family of data acquisition modules.

Learn more about ROI-ISOV10 general purpose 10V bipolar 2 way isolation amplifiers.