Field check using DM70 - DM70 - DMT152

DMT152 User Guide

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User guide
To check the accuracy of DMT152 in the field, you need the following equipment:
  • A fully charged MI70 indicator (the measurement display that is included in the DM70 package).
  • A calibrated reference probe that is suitable for the intended measurement environment and dew point range. You can use a DMP74 probe from the DM70 for dew point down to −60 °C (−76 °F), or a second DMT152 for full measurement range.
  • A connection cable between the DMT152 and the MI70 indicator (Vaisala order code 219980).
  • A reference environment with a stable dew point and temperature in a suitable range for both probes. The normal measurement environment of the transmitter can also be used, if it meets these criteria.
In the procedure described here, the readings of the probes are checked individually. You can also perform the field check so that you connect the reference probe simultaneously with the DMT152 you are checking. In this case, you need two connection cables if you are using a DMT152 also as the reference probe. Also, you must power one of the transmitters by other means than the MI70 indicator.
  1. Place DMT152 in the reference environment (unless it is there already). You can perform the check even if DMT152 is currently being powered and used, as long as there is no cable connected to connector II.
  2. Connect the MI70 connection cable between the MI70 indicator and connector II of DMT152.
  3. Turn on the MI70 indicator. If the analog channels of your DMT152 are configured to use the current output, and if DMT152 is powered by MI70, you will see an error message that indicates the supply voltage is too low for running the actual analog output. This is expected behavior; press OK to acknowledge the error and continue the field check.
  4. Check and adjust the environment settings if prompted. You can change the pressure compensation value (only needed for ppm calculation) and the molar mass of the measurement gas. The pressure must be entered in bara; to enter the value in psia, use the serial line.
    For more information on these settings, see the following sections:
  5. After a brief delay, DMT152 should provide an approximate measurement reading of the selected parameters. Remember that it takes up to 15 minutes for the transmitter to start the active measurement. If the desired parameters are not shown on the display, select them from the Display – Quantities and units menu.
  6. The Auto power off function should be disabled on the MI70 indicator to prevent the indicator from powering off in the middle of the check. While waiting for the active measurement to start, check the setting in the Settings - User Interface menu, and change if necessary.
  7. Write down the Td reading after the measurement has stabilized.
  8. Turn off the MI70 indicator and disconnect DMT152.
  9. Insert the reference probe to the measurement environment, and connect it to the MI70 indicator.
  10. Turn on the MI70 indicator. Check and adjust the environment settings if prompted.
  11. Wait for the reference probe to provide a stable reading, and compare it with the reading from DMT152.

The difference between the readings will give you an indication of the approximate drift of DMT152 and its need for calibration. As a general rule, the reading from DMT152 should be within ±4 °C Td of the reading from the reference probe.

Some notes on using the MI70 indicator with the DMT152:

  • If you disconnect DMT152 while the MI70 indicator is on, the parameters measured will remain on the screen, but no measurement will be shown.
  • The messages from the transmitter (such as the supply voltage error) will appear in English even if MI70 has been set to another language.