C1 & C2 Analogue Voltage Output Option Datasheet

Voltage Output Option 1 Introduction The C1 and C2 sensors have an optional voltage output that is proportional to the averaged CO2 concentration. Key points to note are: • The maximum voltage output (full scale) will always be that applied to pin 3 of the 10 way connector. • Care must be exercised in selecting the load resistance connected between the voltage output (pin 9) and GND (pin 1). • The voltage output pin (pin 9) is an output pin only. Take care not to feed any voltage/current into the voltage output pin. • The voltage output is a factory fit option. It is not present unless requested. • The supply voltage should be 3.3V+/- 0.1V. The sensor can operate at higher voltages, however the offset voltage becomes problematic outside the standard operating voltage range. 2 Voltage Output 2.1 Connections The voltage output is available on pin 9 of the sensor. Power and ground must be applied to pins 1 and 3. C1 Connections, part no. 2112BC1-V C2 Connections, part no. 2112BC2-V EURO-GAS MANAGEMENT SERVICES LTD, REVELSTOKE HOUSE, STOKE ROAD, NOSS MAYO, PLYMOUTH, DEVON PL8 1EY, UK «: +44 (0)1752 872222 Fax: +44 (0)1752 872223 euro-gas@btconnect.com www.euro-gasman.com 11EURO-GAS MANAGEMENT SERVICES LTD, REVELSTOKE HOUSE, STOKE ROAD, NOSS MAYO, PLYMOUTH, DEVON PL8 1EY, UK «: +44 (0)1752 872222 Fax: +44 (0)1752 872223 euro-gas@btconnect.com www.euro-gasman.com 22 2.2 Load Impedance The C1 and C2 voltage output pins have an internal resistance of approximately 150?. The internal capacitance between the voltage output pin and 0V is 220nF. This gives the output a single order high frequency roll off at about 4.8kHz. To avoid loading issues affecting the measurement, it is essential to ensure that load connected to the voltage output pin (9) is greater than 10k? and preferably greater than 100k?. Load Resistance Loading Error 4k7 3% 10k 1.5% 100k 0.1% 500k 0.03% 3 Output Voltage The voltage output is provided by Pulse Width Modulation (PWM) of the sensor supply voltage. This means that all voltage outputs are relative to the supply voltage. For example, if the supply voltage is 3.4V, then the full scale output from the voltage pin will also be 3.4V, the half scale voltage will be 1.7V etc. To convert a voltage into a CO2 concentration: Concentration =FS* Vout/Vsupply Where FS = Full Scale Concentration Vout = voltage output (at pin 9) Vsupply = supply voltage (at pin 3) All voltages relative to GND (pin 1) Note that there is a slight zero offset (see below) which should be taken into account for readings below 10% of the Full Scale. 3.1 Linearity of the Voltage Output Figure 2 shows a typical plot of output voltage (at pin 9) vs CO2 concentration. • Note that the output voltage is linearly dependent on the CO2 concentration measured by the sensor. • Note also that for CO2 concentrations less than 10% of full scale, the sensor output voltage is affected by the output Operation Amplifier offset voltage (~14mV). See above. EURO-GAS MANAGEMENT SERVICES LTD, REVELSTOKE HOUSE, STOKE ROAD, NOSS MAYO, PLYMOUTH, DEVON PL8 1EY, UK «: +44 (0)1752 872222 Fax: +44 (0)1752 872223 euro-gas@btconnect.com www.euro-gasman.com 33EURO-GAS MANAGEMENT SERVICES LTD, REVELSTOKE HOUSE, STOKE ROAD, NOSS MAYO, PLYMOUTH, DEVON PL8 1EY, UK «: +44 (0)1752 872222 Fax: +44 (0)1752 872223 euro-gas@btconnect.com www.euro-gasman.com 44 3.2 Noise on the Voltage Output The typical noise present on the voltage output is as follows with the voltage output at half full scale: • 140µVrms measured in a 20kHz bandwidth. • 450µVrms measured in a 10MHz bandwidth. • In a 10MHz bandwidth the highest noise voltage amplitude is at least 70dB below the desired DC output voltage. 4 Digital outputs The digital (serial) Rx and Tx connections are still available and active when the voltage output is fitted. This allows the sensor to be calibrated and configured over the serial connections. 5 Zero Point Calibration The serial communication options are also available (see the C1 & C2 Sensor Manual). The sensor requires periodic zero point calibration. In many cases, this can be done automatically using the built in auto-calibration option. Additionally, two zero calibration pins area available. Nitrogen Zero (Pin 8) This pin is normally high. Hold it low for 1.5s to trigger a nitrogen zero. This assumes that the sensor is free from any CO2. Ambient Zero (Pin 10) This pin is normally high. Hold it low for 1.5s to trigger an ambient zero. This assumes that the sensor is in fresh air (default setting is 450ppm). 6 Ordering Information The voltage output is a factory fit option and must be specified by the customer at the time of ordering. The customer must also specify the full scale range. Sensors with voltage output have a “V” appended to the product code. For example: part number 2112BC1-V has an analogue voltage output. The data contained in this document is believed to be accurate and reliable. The data given is for guidance only. Euro-Gas Management Services Ltd accepts no liability for any consequential losses, injury or damage resulting from the use of this manual or the information contained in it. Customers should test the sensors under their own conditions to ensure that the sensors are suitable for their own requirements and in accordance with the plans and circumstances of the specific project and any standards/regulations pertaining to the country in which the sensors will be utilised. This manual is not intended to form the basis of a contract and in the interest of product improvement, Euro-Gas reserves the right to alter design features and specifications without notice. 06/11 1 Introduction 2 Voltage Output 2.1 Connections 2.2 Load Impedance 3 Output Voltage 3.1 Linearity of the Voltage Output 3.2 Noise on the Voltage Output 4 Digital outputs 5 Zero Point Calibration 6 Ordering Information