Issue
b3/i2 885, 885-V,, 887 and 887L needs Internal Resistance values for voltage inputs but some devices like SpaceLogic SLA do not publish these values
Product Line
Andover Continuum, EcoStruxure Building Operation
Environment
- b3885, b3885-V, b3887 and b3887L
- i2885, b2885-V, i2887 and i2887L
Cause
These controllers have a pull up resistor that cannot be disabled, unlike most of the i2/b3 range
The below is taken from the b3 technical manual.
Resolution
Not all devices publish the Internal resistance, for example the SpaceLogic SLA, this device has a varying Internal Resistance, but using a value of 25 Ohms, will ensure the maximum error is less than 0.3% of full scale (5ppm for CO2, 0.15 degC)
Generally for most devices, where the internal resistance of a device is not available, it can be calculated by noting the voltage on the output device unconnected, then connected to the i2/b3 device and also noting the actual reading (Temperature, CO2 level, Humidity)
