Other Parts Discussed in Thread: ADS1015,
Tool/software:
Hi TI,
the story:
- multiplexing DC voltages, sourcing with resistor from a 4-20 mA transmittter signals . The sensing resistor is 150 Ohm instead of a 100 Ohm. I supposed this resistor is enough low to cancel the driver amplifier need (is it?)
The setting of the voltage level of the - signal on A/D (voltage divider on low side R12 =192 Ohm, on high side R11 = 4,7 kOhm) results 0,2 V, so the measured value can not be higher than 3,2 V (20 mA x 150 Ohm + 0,2 V)
wiailo_ti1_pdf.pdf
- each channel is selected with two selector (4051): one for the + pole, another for a - pole, for 8 channel each.
- the problem is: giving signal and measuring it on the channel 3, on a pin 2 of the 4051, the measured value changes when I switch a signal onto the channel 6 (ain6+). This happen on both of the 4051s. The change is about 10 mV into minus. The outputs (pin3) are the same. The inhibit of the 4051s are passive continuously (e.g. 0), the channel selection is repeated, but remains unchanged at the next data read from the A/D.
- the JUMPERS are setting with little correction signed with red. It mean the channels 1..5 are two wire 4-20 mA sensors, the others are 3/4 wire similar ones.
My hope was the signals are independent because of the pathing of each channel independent on the PCB but the practice is other. The power source of the transmitter on the ch6 is independent of the VCC1i, e.g. from the power source of the ch3.
This is one of the problems.
The other:
- measured and registrated the signals without any change on the signals (even switching on or off other signals) show a periodical changes showing on the attached spreadsheet.
The A/D is the ADS1015, the circuit diagram is attached too. The A/D panel is from Arduino, ADS1015, from two different producer, the result is the same.
wi_ai_ti1_pdf.pdf
What do I faulty?
Thanks
Laszlo Kannar
