HM34 - Hygrometer VAISALA - Free user manual and instructions

USER MANUAL HM34 VAISALA

Product description Operation Calibration and maintenance Spare parts and accessories Technical specifications

USERS' MANUAL HM34 Relative humidity and temperature meter

1. PRODUCT DESCRIPTION

The HM34 is a battery-operated pocket-size meter for the measurement of ambient relative humidity and temperature. The humidity and temperature sensors are housed at the tip of an extendable probe, where a semipermeable membrane filter protects the humidity probe against water and dust. For easy use, the meter features a HOLD function for the display and an automatic power-off function. For humidity measurement, the HM34 utilizes Vaisala's highaccuracy, high-reliability HUMICAP ® humidity sensor, the Hsensor. Temperature measurement is based on a Pt 100 temperature sensor. The meter is intended for ambient measurements in such applications as: - spot checks - industrial monitoring and inspections - occupational health and safety - laboratory and research use The meter is available with the display calibrated for either degrees Celsius (°C) or degrees Fahrenheit (°F).

1. On/off pushbutton (ON/OFF)

To switch the power on, press the ON/OFF pushbutton. This will automatically start the measurement of relative humidity (%RH).

2. Temp measurement pushbutton (TEMP)

For temperature measurement, press the TEMP pushbutton. TEMP measurement mode is indicated by a (+) or a (-) on the display. Display calibration is either in degrees Celsius (°C) or Fahrenheit (°F) as marked on the sticker on the backside of the meter.

3. RH measurement pushbutton (%RH)

Relative humidity is always positive. If a colon (:) is indicated in front of the displayed reading, the meter reads "negative" RH. This condition may occur e.g. when the meter has not been calibrated after sensor change.

4. Reading hold pushbutton (HOLD)

Pressing the HOLD pushbutton locks the reading in the display. A (s) indicates the HOLD mode. The meter remains in HOLD mode until measurement is resumed by pressing any of the pushbuttons except ON/OFF.

5. Low battery indication

When battery voltage is low, a (B) is displayed. To ensure troublefree operation, replace the battery after about 50 h of operation. Automatic power-off The meter automatically switches off after about 3 minutes, unless a pushbutton is pressed or the meter is set in HOLD mode. Operating voltage The meter uses a standard 9 V transistor battery (type IEC 6F22). The battery is located under a protective lid on the backside of the meter (Fig. 2).

Calibration and maintenance of the meter should be performed at regular intervals which depend on the conditions of use and the desired accuracy, but at least once a year. A one point calibration may be performed for the HM34 meter by adjusting the trimmer potentiometer marked "DRY" (Fig. 2). This field calibration can be performed against a calibrated Vaisala humidity meter. For a higher-accuracy two-point calibration use a Vaisala HMK11 calibrator and saturated salt solutions as described in the Operating Manual of the HMK11. The calibration is done first for the dry end and then for the wet end by adjusting trimmer potentiometers "DRY" and "WET" respectively. The potentiometers are located under the protective lid of the battery compartment (Fig. 2). Replacing the sensors When you replace a defective H-sensor package with a new one, make sure you handle the package with care. After installation, calibrate the humidity sensor. If the "WET" trimmer potentiometer has not been adjusted from its factory setting, a one point calibration is sufficient. Otherwise, perform a two point calibration with an HMK11 calibrator. Replacement of the Pt 100 temperature sensor requires no recalibration.

Chemical tolerance of the humidity sensor (HUMICAP® ) Long-term exposure of the sensor to certain chemicals and gases may shorten its life. The following list gives suggested maximum ambient concentrations for some typical chemicals:

1. Organic solvents:

1000...10 000 ppm (typ.)

2. Aggressive chemicals:

(e.g. strong acids such as SO2,H2SO4, H2S, HCl, Cl2 etc.)

1...10 ppm (typ.) 100...1000 ppm (typ.) 10 000...100 000 ppm (typ.) Detailed information on allowed concentrations are available on request from your Vaisala representative.

Measurement range humidity temperature Accuracy (at +20 °C): (including nonlinearity and hysteresis) relative humidity against factory references against field references 0...100 %RH -20...+60 °C or -4...+140 °F +1 %RH +2 %RH (0...90 %RH) +3 %RH (90...100 %RH) +0.3 °C (+0.5 °F) temperature NOTE: When the HM34 is used in an electromagnetic field of 3 V/m, with the frequency of 200 - 220 Mhz, the temperature deviation is max. ±3 °C. Temperature dependence: Resolution: Response time for humidity (at +20 °C): Display: HOLD function: Supply voltage: Battery operating time: Automatic power-off: +0.04 %RH/°C +0.02 °C/°C

15 s 3 1/2-digit LCD pushbutton hold for displayed value 9 V battery (IEC 6F22) 50 h (typ.) after 3 minutes, unless HOLD is activated

Sensors Humidity: Temperature: Sensor protection: standard optional Weight: Ordering information: HUMICAP® H-sensor (part no. 15202) Pt 100 (1/3 DIN 43760B) plastic grid (part no. 6221) 133 µm sintered filter (part no. 0195) 250 g HM34C (with °C temp. display) HM34F (with °F temp. display) Information and specifications in this manual subject to change without notice. Copyright Vaisala Oy, 1996. HUMICAP is a registered trademark of the Vaisala Company.