Replacing MHT411 - OPT100

Replacing MHT411 Internal Multigas Transmitter Spare Part Instruction
Document code
M212595EN
Revision
B
Language
English
Product
OPT100
Content type
Spare parts
Document type
Spare part manual
  • MHT411 spare part package (Vaisala item code MHT411SP)
  • 29-mm wrench
  • 34-mm wrench
  • Screwdriver with 3-mm-wide (0.12‑in) slotted head
  • 5-mm Allen key
  • Container for waste oil with at least 5 liter (1.3 gallon) capacity
  • Oil absorption material for controlling possible leaks
  • Rags for wiping off oil
CAUTION Before starting, read the maintenance safety section in the OPT100 User Guide (M211858EN). Familiarize yourself with the safety requirements of the installation site.
CAUTION When performing the replacement outdoors, make sure weather conditions allow safe and clean maintenance. The spare parts and the interior of the DGA monitor must remain dry and clean to avoid equipment damage and contamination of the measurement system.
Wear protective eyewear and gloves.
Figure 1. Inside DGA monitor cabinet
1
Cable tray cover
2
Location of connector X16 on the bottom side of the Control Unit
3
Mechanical connection of MHT411
4
MHT411 transmitter
5
MHT411 connection cable
  1. Follow the uninstallation procedure as described in the OPT100 User Guide (M211858EN) up to the point where you select Finish to end the uninstallation sequence.
    This empties the DGA monitor of oil and allows it to be successfully re-initialized after the repair is complete.
  2. Open the OPTPSU power supply cabinet and turn off switch S1 and then circuit breaker F1. This turns off DC power to the DGA monitor. Make sure the DC OK LED on the power supply unit turns off. Close the power supply cabinet when done.
    1
    Circuit breaker F1
    2
    Switch S1
    3
    DC OK LED
  3. Open the DGA monitor cabinet and verify that the LEDs on the door and any LEDs inside the cabinet are off (= power is off). Let the device cool down for 15 minutes before continuing.
  4. Pull out the cable tray cover to remove it.
  5. Follow the MHT411 connection cable to connector X16 on the Control Unit. Note the orientation of the connector. Pull on the connector to disconnect it.
  6. MHT411 is supported by a single mechanical connection to the in-oil measurement block. Hold the 34‑mm nut and turn the 29‑mm nut (the nut that is closer to the MHT411 transmitter housing) counterclockwise to open the connection. Remove the MHT411.
  7. Wipe away any dust and excess oil from the connection area.
    CAUTION Do not use any solvents or cleaning agents to avoid contaminating the DGA monitor with chemicals that could interfere with measurement.
  8. Take the MHT411 spare part (item code MHT411SP) out of its packaging and remove the silicone transport protection covering from the end of the probe head.
  9. Remove the desiccant capsule from the probe head.
  10. Lift the MHT411 into place and tighten the connection by hand. While holding the fitting body steady, rotate the nut with a wrench until you feel a significant increase in resistance. Then turn 1/8 turn more to secure the nut.
    It is recommended to have a second person help you hold the MHT411 and make sure it is mounted straight.
  11. Connect the cable from the new MHT411 to connector X16 on the control unit.
  12. Replace the cable tray cover.
  13. Reconnect the oil lines to the DGA monitor.
  14. Open the OPTPSU power supply cabinet and turn on circuit breaker F1 and then switch S1. Check that the DC OK LED on the power supply turns on. Close the power supply cabinet.
  15. Perform the initialization procedure as described in the OPT100 Installation Guide (M211857EN).
  16. After completing the initialization, close the DGA monitor cabinet and continue with normal measurement for 4 complete cycles. This produces 4 new data points for all measurement parameters. Make sure that:
    • All measurement parameters are produced normally, especially hydrogen and moisture that are measured by the MHT411 transmitter.
    • No errors are shown in the user interface.
    • There are no oil leaks in oil lines or around the MHT411 connection.
  17. MHT411 replacement is now completed. Place the old MHT411 part in the spare part packaging. Return it to Vaisala if return has been requested, or recycle as appropriate.