Hi all,
In one of our designs, we have used ADS1158 to measure the analog inputs. Our design supports both Voltage mode (0-10V) & current mode (0-20mA) on the same analog input. Thus we have used an analog switch, which will connect the analog input to either voltage load or the current load. We have used a 200E fixed resistor as current load & a resistor divider network as a voltage load. Resistor divider will reduce the 10V input range to ADC input range.
Below is the brief block diagram describing the architecture followed for analog input measurement :-
Figure 1
We have a accuracy requirement of 0.1% of FSR at room temperature & 0.2% of FSR over the operating temperature range of -20°C to 70°C. We are performing calibration of analog inputs at room temperature to satisfy the above accuracy requirement.
We are able to achieve the required accuracy over the operating temperature range of 20°C to 70°C when the humidity is set to 0%. But we are facing issue when we test the accuracy at 70°C & 95% humidity. We are observing around 0.3% decrement in accuracy (around 30mV) at 95% humidity. Same behaviour is observed at 95% humidity at 50°C & 60°C.
We have gone through the ADC data-sheet and it does not specify any effect on the accuracy with respect to humidity.
Can you please suggest any reason for this behavior ?
