Onboard device and method for analyzing fluid in a heat engine

A method for controlling a spectrometer for analyzing a product, comprising steps of sending a light beam from a light source of the spectrometer, of transmitting the light beam to a product to be analyzed with which it interacts, and of acquiring 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 acquisition of light intensity measurements comprising steps of:
• 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 measurement of the temperature of the light source, and
• determining, depending on the operation measurements, a value of supply current of the light source, and if the supply current value is within an ideal operating range, supplying the light source with a supply current corresponding to the determined supply current value, and/or
• determining, depending on the operation measurements, a value of integration time of light-sensitive cells of the sensor, and if the integration time value is between threshold values, adjusting the integration time of the light-sensitive cells to the determined integration time value.