continuous operation

[JananiVJ]

Hello dhhagen Thank you for the documentations and library. I am completely new to this and would like to know if anyone managed to get a continuous data output from the OPC.N2 at regular time intervals. Thank you.

[dhhagan]

Hey @JananiVJ Yup. I ran 10 of them for 6 months continuously..just make sure your sampling interval >= 1.2 s otherwise it doesn't behave very well.

[JananiVJ]

When I run the program, the OPC starts and runs continuously. And I get an output in the terminal which looks something like this:

pi@PC-17-0302:~/Documents/examples/opcn2 $ python py-opc.py Alphasense OPC-N2v18.2 True {'Temperature': None, 'Bin 10': 0.0, 'SFR': 3.700000047683716, 'Bin 12': 0.0, 'Bin 13': 0.0, 'Bin 14': 0.0, 'Bin 15': 0.0, 'PM2.5': 0.0, 'Bin1 MToF': 0.0, 'Pressure': None, 'Bin 11': 0.0, 'Bin5 MToF': 0.0, 'PM1': 0.0, 'Bin7 MToF': 0.0, 'Checksum': 0, 'Bin3 MToF': 0.0, 'PM10': 0.0, 'Bin 8': 0.0, 'Bin 9': 0.0, 'Bin 6': 0.0, 'Bin 7': 0.0, 'Bin 4': 0.0, 'Bin 5': 0.0, 'Bin 2': 0.0, 'Bin 3': 0.0, 'Bin 0': 0.0, 'Bin 1': 0.0, 'Sampling Period': 2.7139840126037598} pi@PC-17-0302:~/Documents/examples/opcn2 $

PM values are zero. If I run it again then I get some numbers. How did you manage to get the output data continuously?

[dhhagan]

@JananiVJ It looks like your sampling period is a bit over 2.5 seconds; is that correct? Where are you operating the device?

[JananiVJ]

right now for testing, inside a room. In the future I will install these devices in a fixed sites (outdoor). I will also use them in mobile measurements on vehicles and tethered balloons.

[DancingQuanta]

Could you show your script that runs the OPC?

[JananiVJ]

@DancingQuanta : This is the script that I use to run the OPC

Import the OPCN2 module.

import spidev import opc from time import sleep

Open a SPI connection on CE0

spi = spidev.SpiDev() spi.open(0, 0)

Set the SPI mode and clock speed

spi.mode = 0b01 spi.max_speed_hz = 10000

Send OPc data to SPI interface

to_send = [0x3F] spi.xfer(to_send);

wait a bit.

sleep(1.0)

Print PM (OPC-N2) sensor values

try:
    alpha = opc.OPCN2(spi)
except Exception as e:
    print ("Startup Error: {}".format(e))
print alpha

print alpha.on()
sleep(1.0) #give it time to turn on...

# Read the histogram and print to console
OPC= alpha.histogram()
print (OPC)

Note: in /usr/local/lib/python2.7/dist-packages/opc/init.py

line 76: I set the major and minor versions manually line 243: firmware_max = 18.2 # Maximum firmware version supported