Category: Hardware
Product Number: ADUCM355
Hello,We are currently experiencing 2 problems with the ADUCM355, and would like to ask for some assistance.
Problem 1: When industrial frequency interference exists, it is directly coupled to the DAC output inside the ADUCM355, and the ADC of the collected conductivity jumps in value.
Auxiliary Description: Sampling board and conductivity sensor (2-wires)
Sampling board related circuits are as follows
For a 2-wires conductivity sensor, one signal wire is shorted to the metal case of the sensor itself.
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Detailed description of the related problem:
1. The normal waveform of the DAC (1Vp-p 1Khz frequency, internally configured 1.25V DC bias) output is shown in the following figure.
2. Coupled to the DAC output of the industrial frequency interference
At this time the collected ADC value will appear to jump, such as the normal collection of ADC value of 0.35V, when the interference occurs, then the collected ADC value from 0.35V jumped to 0.28V,It's very short-lived.After that, there is a return to normal values.
Try to solve the solution:
1. Prerequisite notes
> Description of the signal wires</br>
> EC_ADC1：Acquisition of the ADC on the receiving terminal,connect aducm355 pin AIN6,as ADC input;</br>
> EC_ADC2：Acquisition of the ADC on the force terminal,connect aducm355 pin AIN4,as ADC input;</br>
2. Internal switch N9 is on, SE0 is shorted to ground, at this time the waveform is only positive half wave;But the value is stable,The signal is compressed.
3. Internal switch N9 is on, SE0 shorted to Vzero0, then the DAC output complete sine wave, peak-to-peak compression to 0.9 times，the ADC value is stable。
4. Internal switch N4 is on , AIN3 shorted to VREF_1.8V,then the DAC output complete sine wave, peak-to-peak compression to 0.9 times，the ADC value is stable。
- So the N-terminal of the excitation amplifier needs to be connected to a fixed DC level,But the signal is compressed at this point.
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Question 2: Temperature sensor access abnormal
- Internal switch N4 is on , AIN3 shorted to VREF_1.8V.
1. PT100 3-wire mode:
- ambient temperature is stable, normal data is stable for a period of time, then suddenly the temperature increases slowly, all the way up to 100°C (limited value)
- At this time, ADUCM355 is wired as follows:
> constant voltage source ： 100Hz 100mVp-p sine wave
2. PT100 2-wire mode
- The situation is the same as on 3-wires mode.
- The ADUCM355 is wired as follows:
> constant voltage source ： 100Hz 100mVp-p sine wave