Non-integer Bin Values

[jared711]

I've been using the OPC-N2 with a Raspberry Pi 2 Model B. I have purchased a SPI-USB converter as shown in the attached images. The silver USB cable goes to the OPC, and the other USB connections are a keyboard and mouse, and there are several connections from the pins to CO, CO2, NO, and NO2 sensors.

At first, I had an issue with detecting the firmware version. However, I circumvented this by writing a line of code to directly assign the firmware version to 18.2. This may be the reason for the other errors, but since I was using a commercial SPI-USB converter, I didn't think the problem could possibly be bad wiring or poor power supply. The code seemed to work and outputted a histogram, but the numbers didn't make sense. The bin values weren't even integers, as shown in the image below. I believe the problem may come from the fact that I changed the firmware version to get past an error that went a little deeper.

Do I need to get rid of that line of code and hook up the sensor differently, or can I somehow fix these histograms to show me integer values, assuming the bins are supposed to contain integer values?

I'll attach my code in another post.

[jared711]

Here's the code I'm using

!/usr/bin/env python3

Originally from D.H.Hagan https://github.com/dhhagan

Changes made by Jared Blanchard jaredb711@gmail.com

Importing necessary packages

import usbiss import opc import argparse import sys import os import time import csv import datetime import serial

Initiating the OPCN2

try:

Open an SPI connection

spi = usbiss.USBISS("/dev/ttyACM0", 'spi', spi_mode = 2, freq = 500000)
alpha = opc.OPCN2(spi)

except Exception as e: print ("Startup Error: {}".format(e)) sys.exit(1)

Turn on the OPC

alpha.on()

Wait for ten seconds to allow the sensor to boot up

time.sleep(10)

#change firmware to correct version
alpha.firmware = {'major': 18, 'version': 18.2, 'minor': 2}

Find the appropriate number to assigne to the filename

files = os.listdir('/home/pi/Desktop/PMdata') number=1 for i in range(0, len(files)): string = files[i] string = string[:-4] #eliminate the .csv at the end index = 0 for letter in string: if not letter.isalpha(): index = index*10 + int(letter) #make sure the tens and hundreds places are accounted for if index >= number: number = index + 1

Create a .csv file with the appropriate number in its name

file_name = '/home/pi/Desktop/PMdata/OPCdata%s.csv' % (number) file_csv = open(file_name,'w') csv = csv.writer(file_csv, delimiter=',')

for i in range(1,5,1):

print the file number at the beginning of each histogram

file_number = 'file number: %s' % (number)
print (file_number)

# Read the histogram and print to console
for key, value in alpha.histogram().items():
    #separated by commas
    data=[i, key, value]
    csv.writerows([data])        
    print ("i: {}\tKey: {}\tValue: {}".format(i, key, value))

""" Other values that can be read from the OPC-N2 n = alpha.sn() #Serial Number print(n) alpha.read_firmware() """

close the file

file_csv.close()

Shut down the opc

alpha.off()

[dhhagan]

Hey @jared711 great questions! If you are using a recent version of the library (I think you are) then the histogram reports numbers in number concentration (#/cc) as mentioned in the docs. If you want to get the raw histogram values, you can add the argumenent number_concentration=False.

So, for raw values:

alpha.histogram(number_concentration=False)

For values in actual number concentration:

alpha.histogram()

Otherwise, your numbers look fine by first glance. Let me know if you have any other questions.

[dhhagan]

Hey @jared711 Did this solution work for you?

[jared711]

Yes, it worked great for me! Thanks for the quick response!