Ohmic instruments DM-509 Series User manual

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direct sunlight.
4. After 2 hours check the instrument reading; it should be 12% ± 2%.
If readjustment is necessary:
Model 509-1/2: Remove 4 screws on back of instrument; gently open hous-
ing. See Figure 1 for pot location.
Model 509-3/4: Remove screw from probe housing and gently pull out the
PC board. See Figure 2 for the location of the potentiome-
ters. To readjust the pots without removing the probe hous-
ing you can drill through the two prepared holes, situated in
the middle of the housing.
5. Adjust the zero potentiometer for a reading of 12% RH.
6. Replace the 12% RH bottle with the 90% bottle. Close the 12% bottle.
7. Wait for 2 hours and check instrument reading; it should be 90%, ± 2%.
8. If necessary, readjust the span potentiometer for a 90% RH reading.
9. Repeat Steps 5 through 8 until both readings are correct; when that happens
the meter will meet its original accuracy specification. Close the bottles im-
mediately after use and wash your hands; the bottles can contain poisonous
solutions. Reassemble the housing.
Calibration Standards
Each unit is calibrated against standards traceable to the National Institute of
Standards and Technology.
Calibration certificates
In addition to the normal calibration procedure, each unit can be supplied with its
own traceable calibration certificate.
Calibration interval time
Under normal ambient conditions (0 to 50°C, 0 to 70% RH) and for an accuracy of
± 2% RH, we recommend an annual calibration. For an accuracy ±5% RH we
recommend calibration every five years. For environments with airborne chemi-
cals or for high humidity and high temperature conditions we recommend more
frequent calibration.
Limited Warranty
This product is warranted by Ohmic Instruments Company to be free of defects in
material and workmanship for one year after delivery. A product found to be de-
fective for these reasons within this period will be repaired or replaced free of
charge by Ohmic. We give no other warranties. Ohmic Instruments Co. shall not
be liable for any damages or losses, whether direct or indirect. The warranty can-
not be transferred or assigned to third parties.
1
508 August Street Easton, MD 21601
www.ohmicinstruments.com
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Instruction Manual for Relative Humidity
& Temperature Meter DM-509
Introduction
The DM-509 series of digital handheld meters are designed to indicate the relative
humidity or temperature of the ambient air. Featuring auto power-off and a large
3½ digit LCD display, the meter is standard equipped with a fast reaponse capaci-
tive sensor with a working range of 10 to 95% RH. Accessories like calibration
bottles or carrying cases are available from Ohmic.
Description
Digital meter with fixed probe, temperature in °C DM-509-M-01 ——
Digital meter with fixed probe, temperature in °F DM-509-M-02 ——
Digital meter with separate probe, temperature in °C DM-509-M-03 DM-509-T-03
Digital meter with separate probe, temperature in °F DM-509-M-04 DM-509-T-04
Model

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DM-509.PUB
Measuring range
Working range
Resolution % RH
Accuracy @ 25°C typ.
Temperature drift
Response time
Measuring range temperature
Resolution temperature
Accuracy temperature
Power supply
Auto power-off
Low battery
Battery life
Operating temperature
Weight
Display
0 to 100% RH
5 to 95% RH
0.1% RH
± 2% RH (10 to 95% RH)
0.05% RH/°C typical
10 sec. for 90% of the change (air velocity 1 m/s)
-20 to +60°C
0.1°C
± 0.2°C ± 1 digit
9V alkaline battery
Approx. 12 minutes
BAT indication on display
Approx. 200 hours (alkaline battery)
-20 to +60°C (-4 to +140°F)
0.45 lb. (0.2Kg)
3½ digit 0.39” (10mm)
3
Auto shut-off
The DM-509 is equipped with an auto shut-off switch. To modify for manual on-off
operation, remove jumper J5 on the PC board inside the instrument. Refer to Fig-
ure 1 for the location.
Battery
The DM-509 uses a 9 volt alkaline battery. If the word BAT appears on the dis-
play, the battery should be replaced.
If the unit will not be used for an extended period, remove the battery.
Calibration Procedure
Recalibration intervals depend on environmental conditions; generally every 12
months is recommended. Calibration should be done only by a qualified techni-
cian. Calibration bottles can be used, or better yet, a traceable humidity reference
simulator like the S-503, available from Ohmic. The bottles contain a saturated
salt solution with standard relative humidity. Use 12% RH for zero calibration and
90% RH for span calibration.
Output signal adjustment is made by the “zero” and “span” potentiometers. For pot
locations see Figure 1 for the 509-1/2 and Figure 2 for the 509-3/4.
1. Do not remove the slotted cap from the probe during calibration.
2. Visually check the sensor for damage or corrosion. Do not touch the sen-
sor!
3. Open the 12% bottle and immediately put the probe into the bottle. It is es-
sential to keep the bottle at a constant temperature of about 20°C (68°F). The
humidity is temperature dependent; do not heat the bottle and avoid Cont’d
Figure 1: Location of potentiometers on DM 509-1 and –2
Figure 2: Location of potentiometers on RH probe (DM-509-3 and –4)