Issue
Input scaling issues with the use of 0 to 5 Vdc and 0 (or 4) to 20 Milliamp transducers on a MNB controller.
Environment
MNB Series Controller application program using Analog Input voltage or current inputs.
Cause
The resolution of the Analog Input object value is determined by the maximum value that can be processed.
If the scaled input range is less than 163.84, the output resolution is 0.01
If the scaled input range is greater than 163.84, the output is an integer value.
Resolution
When programming the Analog Input object in the WorkPlace Tech Tool, it is important to properly configure the input range and scaled value range for this object.
If configured for a 0 to 5 VDC input, the sensor properties must be configured as follows:
Input Sensor Type (Type): 5 - Volts
Input Low Value (LInput): 0
Scaled Low Value (LScale): 0
Input High Value (HInput): 5
Scaled High Value (HScale): (value, up to 16383, corresponding to 5 volt input) See note below.
If configured for a 0 to 20 milliamp or 4 to 20 milliamp input, the sensor properties must be configured as follows:
Input Sensor Type (Type): 4 - Milliamp
Input Low Value (LInput): 0 or 4 (depending on transducer)
Scaled Low Value (LScale): 0 (value corresponding to LInput sensed value)
Input High Value (HInput): 20
Scaled High Value (HScale): (value, up to 16383, corresponding to 20 milliamp input) See note below.
NOTE: The HScale value should be set to give an output value for the Analog Input object that corresponds to the maximum temperature, flow, cfm, etc. that the sensor is measuring. The resolution of the value processed by this object must be taken into account when setting the HScale value because the input to output scaling and precision depends on this scaling constant. If the HScale value is less than 163.83, the input resolution is two decimal places and if greater than 163.83, integer resolution. An example of where this scale range is critical would be the use of a 0 to 5 volt air pressure transducer measuring an air pressure of 0 to 2 InWC. If the HScale is set to 2, the output would only resolve to 0.01. If the HScale value were set to 2000, the output would be in thousandths of an InWC, giving you an effective resolution of 0.001. Since this value is one thousand times the actual measured pressure, this 1000x scale factor would also have to be taken into account in any use of that value within the application.
