Vaisala Oyj Humidity/Temperature Transmitter HMT120

Ensure the filter is not cleaned but replaced

Open the transmitter cover to access the buttons and LEDs

Identify the buttons and LEDs on the HMT120 motherboard

Press and hold the ADJ button until the green LED blinks slowly

Do you wish to perform the RH adjustment?

Remove the filter and insert the probe into the dry end reference chamber

Wait for conditions to stabilize (approximately 30 minutes)

Press the - or + button to adjust Iout current, then press ADJ button again

Ensure all necessary equipment is available

Connect the HMI41 to the HMT120 using the connection cable

Is the HMI41 turned on and displaying text?

Press the ON/OFF button on HMI41 until text appears

Press both ENTER and MODE buttons within 1-2 seconds

Select number 3 for calibration with buttons A and V, then press ENTER

Loosen the metal locking bushing by carefully turning it counter clockwise.

Remove the probe from the transmitter by pulling it gently downwards.

Attach the new probe to the four pin M8 panel connector at the transmitter (only one position possible).

Tighten the locking bushing to the M8 panel connector by turning it clockwise.

Ensure you have the calibrator kit for calibration against saturated salt solutions.

Verify availability of HMK15 Humidity Calibrator and pre-measured certified salts from Vaisala.

Check if portable humidity meters HM70 or HMI41 are available for use.

Select the calibration method to use

Calibrate the HMT120 using the selected method.

Is the probe within its adjustment/trim range?

If the probe is outside its adjustment/trim range, was the probe changed or Vaisala Services contacted?