Power Supply Sensitivity
System engineers use signal conditioning module (SCM) transfer functions as ratios of module outputs to sensor inputs in terms of units applicable to their particular system applications. For example; volts per degree, milliamps per psi, volts per inch, milliamps per gpm, etc. System error budgets should always be initially analyzed to ensure that the combined impact of changes in environmental conditions such as temperature, moisture, vibration, time, induced noise, and supply voltage on SCM errors are within acceptable system error limits.

SCMs and electrically energized field sensors are sensitive to changes in supply voltage, often overlooked in error budgets. Dataforth’s power supply sensitivity specifications (PSS) are generally referred to the input (RTI) and have negligible effect on module outputs in most situations. Some illustrative examples are;

(a) SCM5B40, analog input voltage module with ± 10mV input to ±5V output and a PSS RTI of ± 2µV per % change in power supply voltage has a ±0.02% change in output voltage for a ±1% change in module power supply voltage;

(b) SCM5B32, analog input current module using a 20 ohm sense resistor with 0-20mA input to 0-5V output and a PSS RTI of ±20µV per % change in power supply voltage has a ±0.005% change in output voltage for a ±1% change in module power supply voltage and

(c) SCM5B33, isolated true RMS module with a PSS referred to the output of ±200 ppm (parts per million) per % change in power supply voltage has a ±0.02% change in output voltage for a ±1% change in module power supply voltage.
Consider a SCM5B32 with a ±0.1% variation in power supply voltage. The module PSS error in output would be ±0.0005% and is clearly negligible. Modern power supplies for SCM applications are very stable and have only fractions of % changes in their voltage outputs during normal operation; however, these supplies may be purchased with outputs, which are not exactly 5 volts. Dataforth’s low PSS designs ensure that their SCM specifications remain valid for power supply voltages within the 4.75-5.25V range.

All Dataforth signal conditioner product data sheets include Power Supply Sensitivity specifications. Moreover, modules are shipped with serialized test reports to verify performance and to validate that the modules meet the published data sheet specifications.

Here's an example of a typical Dataforth product data sheet and serialized test report --
Dataforth DIN mount module for Thermocouple inputs (170kb pdf file)
Dataforth Test Report example shipped with each module (78kb pdf file)

Remember, our Application Engineers can assist you with signal conditioner selection over the phone or via fax and email. Call us at our manufacturing facility in Tucson at 520-741-1404 (fax 520-741-0762) or Email us at techinfo@dataforth.com.
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