12 • Chapter 2: Description HS-04 Operator’s Manual
Sensor
The H
2
S sensor is an electrochemical cell that consists of two precious metal electrodes in a dilute
acid electrolyte. A gas permeable membrane covers the sensor face and allows gas to diffuse into
the electrolyte. The gas reacts in the sensor and produces a current proportional to the
concentration of the target gas. The HS-04’s circuitry amplifies the current, converts the current to
a gas concentration, and displays the concentration on the LCD.
Filters
Humidity Filter
A white humidity filter is placed into a recess in the filter gasket over the H
2
S sensor. The filter
absorbs humidity in the sampling environment to prevent unstable readings around 0 ppm.
• For users with a 1 ppm H
2
S alarm setpoint, the filter should be replaced every 6 months if
you notice a drift on the zero reading or if the filter appears dirty (whichever is sooner).
• For users with a 2 ppm or higher H
2
S alarm setpoint, the filter does not necessarily ever
need to be replaced.
Hydrophobic Filter
The white, circular hydrophobic filter fits into a recessed area in the front case and is held in place
by the sensor gasket. It prevents water and particulates from entering the instrument.
Infrared Communications Port
An infrared (IR) communications port is located at the top of the instrument, near the LED.
Logged data transmits through the port in standard IrDA protocol. A computer’s infrared port or
an IrDA/USB cable connected to a USB port can be used to download data to the 04 Series
Datalogging Program. See the 04 Series Datalogging Program operator’s manual for data logging
and downloading instructions.
Batteries
2 AAA batteries (alkaline or Ni-MH) power the HS-04. At 25°C alkaline batteries will last at least
9,000 hours (375 days) and Ni-MH batteries will last at least 6,000 hours (250 days). The battery
icon in the upper right of the LCD shows remaining battery life.
A low battery warning activates when the HS-04 detects a low battery voltage. The HS-04 sounds
a dead battery alarm when battery voltage is too low for Measuring Mode.
WARNING: Use only Duracell MN2400 or PC2400 or Eneloop BK-4MCC batteries to
maintain the QPS classification of the HS-04. Use of other batteries will void the
QPS classification and may void the warranty. Do not mix old/new or different
types of batteries.
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