Hi everyone,
I’ve been trying to get the 968-006 up and running but seem to have run into a small problem, the readings it give off are way above the possible values. After more than 1 hour of ‘Power-On Stabilization Time’ the sensor returns a measured ppm of around 5. For the record 0.5 ppm SO2 will kill you within 3 hours.
I used the library created by the developers: GitHub - SPEC-Sensors/ULPSM: Public Arduino Library for ULPSM (ultra-low power sensor module) or SDK (sensor development kit)
And used the recommended 2x 10k ohm voltage ladders, as can be seen in my setup in the image blow.
I modified the code slightly to work with the voltage ladder, this is the code I use:
/*
ULP.cpp - Library for reading SPEC Sensors ULP.
Revised by David E. Peaslee, May 22, 2020.
Created by David E. Peaslee, OCT 27, 2016.
Released into the public domain.
*/
#include "Arduino.h"
#include "ULP.h"
// These constants won't change. They're used to give names to the pins used and to the sensitivity factors of the sensors:
const int C1 = A0;
const int T1 = A3;
//averaging times, keep these low, so that the ADC read does not overflow 32 bits. For example n = 5 reads ADC 4465 times which could add to 22bit number.
const int n = 5; //number of seconds to read gas sensor
const int m = 1; //number of seconds to read temperature sensor
const int s = 10; //number of seconds to read all sensors should be greater than n+m+1
const float Sf1 = 11.61; //nA/ppm change this to match your barcode!!!!
unsigned long etime;
SO2 sensor1(C1, T1, Sf1);
// Include these if using different boards with different voltages
void setup() {
//uncomment only after you have connected 3.3V to Aref on the arduino
analogReference(EXTERNAL);
sensor1.pVcc = 3.31; //analogRead Reference Voltage, equal to pVsup when analogReference uses same voltage as sensor power
//sensor1.pVcc = 5.04; //analogRead Reference Voltage, maybe measure Aref??
sensor1.pVsup = 3.31; //voltage supplied to V+ of ULP, default is 3.3 Volts, probably should measure this as well.
sensor1.pVref = 1650;
Serial.flush();
Serial.begin(9600); // initialize serial communications at 9600 bps:
Serial.println();
Serial.println("Setting Up.");
Serial.print("Vsup for all sensors = ");
Serial.println(sensor1.pVsup);
Serial.print("Vcc for all sensors = ");
Serial.println(sensor1.pVcc);
Serial.print("Vref for sensor 1 = ");
Serial.println(sensor1.pVref);
// Using resistor values from board R1, R2, R3 are for setting pVref and Bias, while R6 sets the gain
// If using modified or custom boards set Vref and Gain like this
//long int R2 = 1000; //Assumes R1 and R3 are 1 MOhms in resistor ladder
//float bias = -25.0
//sensor2.setVref(bias, R2);
//sensor2.pGain = 100000; //resistor R6
//if you know the V_ref replace the following code...
Serial.println("Remove Sensor.");
if (sensor1.OCzero(n)) {
Serial.print("Vref new = ");
Serial.println(sensor1.pVref_set);
} else {
Serial.println("Recheck Settings, Zero out of range");
while (1) {
Serial.println(analogRead(A0));
delay(1000);
}
}
//...with this code and your measured value of new Vref
//sensor1.pVref_set = ????
//sensor1.setXSpan(); //Must have previously zeroed in clean air, returns new span factor.
//When calibrating the temperature use "LOW"/"HIGH" for the temperature range ie .setTSpan(40.2, "HIGH") where T is the current high temperature
//sensor1.setTSpan((71 - 32.0) * 5.0 / 9.0, "LOW");
Serial.println("Finished Setting Up, Replace Sensor Now.");
Serial.println("T1, mV, nA, C1");
etime = millis();
}
void loop() {
while (Serial.available()) {
if (Serial.read() == 'Z') {
Serial.println("Zeroing");
sensor1.zero(); //Uses last values read of Izero and Tzero
Serial.print("Izero, Tzero: ");
Serial.print(sensor1.pIzero);
Serial.print(", ");
Serial.println(sensor1.pTzero);
}
}
if (millis() - etime > (s * 1000)) {//also handles case where millis rolls over, but may cause timing issue.
etime = millis();
sensor1.getIgas(n);
sensor1.getTemp(m);
sensor1.getConc(sensor1.pT);
Serial.print(sensor1.convertT('C')); //use 'C' or 'F' for units
Serial.print(", ");
Serial.print(sensor1.pVgas);
Serial.print(", ");
Serial.print(sensor1.pInA);
Serial.print(", ");
Serial.println(sensor1.convertX('M')); //use 'M' or 'B' for units or Serial.println(sensor1.pX); to just print ppb
}
}
Could anybody help me figure out why the ppm readings are so high? Thanks in advance!
