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Supply voltage considerations for pressure transmitters
1st September 2007
In order to convert a current output to a voltage signal for a analogue voltage input card it is necessary to add a load resistor in series with the current loop and use the resulting voltage drop across the load resistor as the input signal.
For example a 250 ohm resistor would produce a 1 volt output at 4 mA and a 5 volt output at 20 mA. Therefore a pressure transmitter that requires a minimum of 10 volts to operate within specification limits would need a power supply of at least 15 volts. Most manufacturers do not specify the extra voltage required for the voltage drop across the load resistor and only state the range of voltage required to power the pressure transmitter directly. It is important to consider the extra voltage required for the drop across the load resistor on a 2 wire current loop otherwise there may not be enough voltage left to power the pressure transmitter directly. Some pressure transmitter data sheets include a graph or formula to help you calculate the required power supply voltage when using a load resistance.
Related Products Pressure transmitters with 2 wire 4 to 20mA current loop outputs Digital readouts for powering and measuring 4 to 20mA pressure sensors Plug on current loop powered digital indicators for pressure transmitters
Associated Topics Difference between a pressure transducer and transmitter
Resources Glossary of terms for pressure transmitters 4-20 mA current output explanation
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