Onboard device and method for analyzing fluid in a heat engine

A spectrometer comprising a light source emitting a light beam, a sensor comprising light-sensitive cells disposed on a route of the light beam after it has interacted with a product to be analyzed, and a control device controlling a supply current of the light source, and an integration time of the light-sensitive cells,

• wherein the control device is configured to:
• send a light beam from a light source of the spectrometer,
• transmit the light beam to a product to be analyzed with which it interacts, and
• acquire light intensity measurements enabling a spectrum to be formed, by means of a sensor of the spectrometer, disposed on a route of the light beam after it has interacted with the product to be analyzed, the spectrometer being configured to acquire light intensity measurements by:
• acquiring in the presence of the product to be analyzed measurements representative of the operation of the light source and independent of the product to be analyzed, the operation measurements comprising a measure of a temperature of the light source, and
• determining, depending on the operation measurements, a value of integration time of light-sensitive cells of the sensor, and when the integration time value is between threshold values, adjusting the integration time of the light-sensitive cells to the determined integration time value
• determine an integration time value applied to light-sensitive cells of the sensor:
• compare the integration time value to threshold values;
• and
• when the integration time value is not within the threshold values, adjusting a new value of the supply current of the light source such that the integration time value is within the threshold values, and when the supply current value is within the ideal operating range, supplying a supply current corresponding to the determined supply current value to the light source.