User manual VAISALA HMD70Y

[. . . ] 4 Electrical connections and installation of the current module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. 4. 1 Connection to an AC supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] The HMD70U/Y transmitters are easy to install and maintain: the electronics can be disconnected without dismantling the installation. One point calibration is easily performed with the HMI41 indicator and the calibration cable 19116ZZ. Both transmitter types incorporate the HUMICAP®180 humidity sensor which uses an operating principle based on changes in the capacitance of a thin polymer film as it absorbs water molecules. The HMD70Y transmitters measure temperature with the reliable Pt 1000 sensor. 1997-07-31 1 HMD70U/Y Transmitters Operating Manual U303en-1. 1 2. TO BE NOTED WHEN MEASURING HUMIDITY In the measurement of humidity and especially in calibration, it is essential that the temperature equilibrium is reached. Even a slight difference in the temperature between the measured object and the sensor causes an error. For example, at +20 °C (+ 68 °F) and 50 %RH, a temperature difference of +1 °C between the measured object and the sensor causes an error of +3 %RH. If relative humidity is 90 %RH, the error is about +5. 4 %RH. The error is at its greatest when the temperature of the sensor differs from that of the surroundings and the humidity is high. A few degrees' difference in temperature may cause water to condense on sensor surface. Efficient ventilation accelerates evaporation whereas in an unventilated space, it may take hours. The HUMICAP®180 sensor returns to its normal functioning as soon as water has evaporated. Any contaminated water condensing on the sensor may shorten its life span and change the calibration. 10 9 8 7 dRH (%RH) 6 5 4 3 2 1 0 -40 -20 0 20 40 60 80 100 Temperature (°C) Figure 2. 1 Measurement error at 100 %RH when the temperature difference between the ambient and the sensor is 1 °C 2 1997-07-31 U303en-1. 1 HMD70U/Y Transmitters Operating Manual 3. 3. 1 INSTALLATION Selecting the place of installation Select a place that gives a true picture of the environment or process and is as clean as possible. Air should circulate freely around the sensor. A rapid air flow is recommended as it ensures the same temperature for the ambient air and the sensor head. Install the transmitter in a place where no cold or hot spot can develop. If the sensor head is installed in a duct or channel where the temperature is different from the ambient temperature, insulate the point of entry. An uninsulated installation might lead to condensation on the sensor head and even if no condensation occurs, the resultant air flow may change the temperature near the sensor head and distort the readings. 3. 2 Mounting Mount the transmitter with two screws. Place the drilling template on the duct surface and drill the holes as indicated. Remember to drill an additional hole for calibration purposes. 62 (2. 44) 250 (9. 84) 100 (3. 94) (3. 23) >>> <<< Mounting hole 82 (3. 23) Figure 3. 2 Dimensions of the HMD70U/Y (in mm) 1997-07-31 Mounting hole 82 Ø 12 (0. 47) 100 (3. 94) 3 HMD70U/Y Transmitters Operating Manual U303en-1. 1 3. 3 Grounding Open the lid and mount the cable bushing set 18941HM. Do the grounding according to Figure 3. 3. When connecting the signal cable to the transmitter housing, fold the cable braid between the brass disk in order to achieve the best possible EMC performance. Do not leave the bare shield of the connected wires so that it can shortcircuit the electronics! flexible wires 0. 5 mm² (AWG 20), stranded wires recommended 3 140 braid brass disks rubber ring nut D = Ø 7. . . 10mm (If the cable diameter is less than 7mm, use a shrinking tube or an adhesive tape) 165 shielding tube braid 25 brass disks cable Figure 3. 3 Signal cable grounding with bushing 18941HM 4 1997-07-31 U303en-1. 1 HMD70U/Y Transmitters Operating Manual 3. 4 Electrical connections and installation of the current module Figure 3. 4 shows the electrical connections and the installation of the current module. INSTALLATION OF THE CURRENT MODULE 18945HM OUTPUT SELECTIONS T 0. . . 1V RH 0. . . 5V 0. . . 10V 0. . . 20mA current module T RH T RH T RH 1. [. . . ] · Use the RH offset potentiometer (Figure 3. 4. ) to adjust the output signal to the value given in the calibration table (Chapter 4. 3). · Place the probe into the calibration hole of the NaCl bottle in the calibrator. · Check that the reading corresponds within the desired accuracy to the reading given in the calibration table. If not, adjust the reading with the RH gain potentiometer (Figure 3. 4). [. . . ]