Support Circuits (PPM) & (PPB)

Support Circuits (PPM)

Alphasense offer 4-20 transmitter boards to measure toxic gas, carbon dioxide and oxygen concentrations for use in fixed installation systems.

The 4-20mA digital boards can be used with all Alphasense toxic gas sensors whilst the analogue boards are suitable for most Alphasense oxygen sensors and unbiased B series toxic gas sensors. Both boards have the same dimensions, pillar locations, 2-wire current loop connectors and 4-20 mA output.

The 4-20 mA current is linear from 0 ppm (4 mA) to your specified full-scale concentration (20 mA). The voltage measured across a resistor in series with the supply current (typically 100 ohms load resistor) will give an accurate measurement of gas concentration.

The boards supplied with sensors are pre-calibrated to customer requirements. The 4-20 mA output signal provides an equivalent performance to that shown in the individual sensor Technical Data Sheets but scaled to your specific range requirements.

Alphasense NDIR transmitter boards offer both 4-20 mA and USB outputs, scaled to one of four ranges. Concentration range can be recalibrated via PC/ USB port using our proprietary software.

To allow OEMs to distinguish their product from other offerings, the sensor-to-gas aperture design is left for the OEM to execute.

Application Notes

Download Toxic Application Notes – see application notes for full details.

Support Circuits (PPM)

Support Circuits (PPB)

Alphasense offer support circuits for the new ranges of A4 and B4 four-electrode sensors, together with a 4-20mA transmitter board for our NDIR CO2 infrared sensor.

Individual Sensor Boards (ISBs) have been built with lowest noise for the new B4 family of sensors, designed where best resolution at low ppb levels is required in permanent fixed site networks. Requiring 3.5 to 6.4 VDC input, they provide buffered voltage output from both the working and auxiliary electrodes. Boards are pre-configured when you order for the type of sensor, with fixed zero and electronic gain. Each ISB supports one B4 sensor and requires less than 1.5 mA power.

The Analogue Front End (AFE) family of circuits is designed for use with the Alphasense A4 family of four-electrode gas sensors where space is critical, such as with mobile air quality monitors. Options include a 2-sensor AFE, 3-sensor AFE and 3-sensor +PID AFE. All circuits include a low noise bandgap to provide 200 mV bias voltage for NO sensors. Requiring from 3.5 to 6.4 VDC supply, the 3-sensor board for example only needs 2 mA power.

Each board includes a Pt1000, providing 1mV/K signal for your software temperature corrections. The AFE can measure both oxidising (CO, H2S, NO, SO2) and reducing (O3, NO2) gas sensors; AFE configuration is specified when ordering.

Alphasense NDIR transmitter boards offer both 4-20mA and USB outputs.  Concentration ranges can be recalibrated via PC/USB port using our proprietary software.

A range of gas hoods, mounting kits and cable is also available for use with Alphasense support circuits.

Application Notes

Download Application Notes – see application notes for full details.

Support Circuits (PPB)