The HMM 30D is part of Vaisala’s humidity transmitter line for environmental chamber applications, utilizing Vaisala’s HUMICAP® humidity sensor technology.
Figure 1: Vaisala HMM 30D
As the HMM 30D is a humidity transmitter, it relies on an internal sensor to take the measurements. The HMM 30D utilizes the Vaisala HUMICAP®K sensor, a capacitive thin-film capacitive humidity sensor. The thin-film polymer either absorbs or releases water vapor as the relative humidity of the ambient air rises or drops. The dielectric properties of the polymer film depend on the amount of water contained in it: as the relative humidity changes, the dielectric properties of the film change, and so the capacitance of the sensor changes. The electronics of the instrument convert the capacitance into a current or voltage output which indicates the humidity.
A number of variations exist for the HMM 30D model. These variations consist of different input and output power options, as well as output quantities. With regard to input and output power options, it is possible to configure the model to accept a power input of 14-35 VDC, 19-35 VDC, 20-35 VDC, or 12-24, 16-24, 9-24, 17-24 VAC, and an analog output signal of either either 0-5 VDC, 0-10 VDC, or 0-20 mA. These operating configurations and specifications can be changed by the user by augmenting the jumper configuration.
As is, the HMM 30D can be integrated into equipment to work with the NI WSN in environmental chamber applications.