User`s manual

MDL-DataManager™ Reference Guide Architectural Energy Corporation
Appendix B – Calculating Scale Factors 34
Appendix B – Calculating Scale Factors
Architectural Energy Corporation (AEC) stocks signal conditioning modules for use
with a wide array of AEC-supplied or third-party sensors. These different signal
conditioning modules allow the MicroDataLogger unit (MDL) to connect to nearly any
sensor or meter on the market based on the sensor or meter output signal. Each
separate sensor or meter to be used with the MicroDataLogger data acquisition
system will require a module to connect to the MDL to the sensor. It is important to
note that AEC carries a number of sensors that are pre-wired to modules for your use:
temperature, humidity, occupancy, and lite level.
Conversion
Formula
Sensors and transducers converta physical input (pressure, amperage, etc.) into an
electrical signal (volts, milliamps, pulses, etc.) that can be measured by the
MicroDataLogger unit (MDL). For the MDL to accurately read the signal connected to
it and record a corresponding electrical signal, a Slope and Offset need to be
calculated and entered into the configuration of the MDL.
The conversion formula for this is shown below:
Reading in Engineering Units = (Sensor or Transducer Output ) x ((Slope) + Offset)
Or, Reading in Engineering Units is (y = mx + b).
Determining
Slope
Examining the equation of the line (y = mx + b) created by comparing the
Sensor/Transducer Input (y) against the Sensor/Transducer Output (x), we can
determine the Slope (m). The Slope, then, is determined by the following formula:
Slope = Full Scale Range or Transducer in Engineering Units
Full Scale Output Signal Range of Sensor or Transducer (voltage, current)
Example: You are using a 150 psig pressure transducer that has a 1-5 volt output
signal.
150 psig Maximum Range less 0 psig Minimum Range = 150 psig
5 volt Max. Output Range less 1 volt Min. Range = 4 volts
Therefore, Slope = 150
= 37.5
4
Determining
Offset
To determine the Offset (b), we examine the line when the input is at a minimum.
Thus, when y = y min, we have y min = mx + b. Solving for b yields b = y min - mx.
Consequently we have:
Offset = (Minimum Sensor/Transducer Input Value in Eng. Units) – ((Slope) x
(Sensor/Transducer Output* at Minimum Input Value))
*Voltage, etc.
Example: You are using the same 150 psig pressure transducer that has a 1-5 volt
output signal.
Therefore, Offset = 0 – ( 37.5 x 1 volt) = 0 – (37.5) = -37.5