RKI Instruments OX-94 Manuale utente

INSTRUCTION MANUAL

RKI INSTRUMENTS, INC.

MODELS: OX-94, CO-94, HS-94

PORTABLE SINGLE GAS MONITORS

RKI Instruments, Inc.

33248 Central Ave.

Union City, CA 94587

(510) 441-5656

INTRODUCTION

The RKI Models OX-94, CO-94, and HS-94 (the 94 series) are compact portable gas

detection instruments. They are designed to protect the worker from dangerous gas

levels, and are also intended to be used as survey tools to determine gas levels in a

workspace or other confined space. These instruments offer a full range of features,

including:

• Continuous detection of one of three hazards.

Oxygen Deficiency (OX-94)

Carbon Monoxide levels (CO-94)

Hydrogen Sulfide levels (HS-94)

• Large LCD readout with backlighting for dark areas and with easy to understand

symbols for Battery Condition, Peak Hold, STEL, and TWA.

• Loud audible alarm, directed upward for easier hearing.

• Intrinsically Safe design for Class I, Division 1, Groups A,B,C, and D hazardous

atmospheres.

• Microprocessor control for reliability, ease of use, and advanced capabilities.

• Small, lightweight design for user comfort.

WARNING

These instruments are designed to detect potentially life threatening gas levels.

Users must follow the instructions and warnings of this manual to assure proper

and safe operation of the instrument.

DESCRIPTION

The RKI Models OX-94, CO-94, and HS-94 are advanced portable instruments for

detection of either Oxygen Deficiency levels, Carbon Monoxide levels, or Hydrogen

Sulfide levels. Each instrument version is capable of detecting one type of gas. See Table

1 for the detection ranges. Gas detection features include audible alarm and blinking

display for dangerous gas concentrations, time weighted averaging for exposure to

toxic gases (CO or H2S), a Peak Hold function for toxic gases, and minimum hold

function for Oxygen detection.

The 94 series instruments are very compact to easily fit in a shirt pocket or on a belt. It

also comes equipped with a lanyard which can be used to hang the instrument from the

users shoulder or to wear around ones neck. The 94 series also comes equipped with a

vinyl carrying case for added protection and durability.

The 94 series is housed in a rugged water resistant plastic housing, and has a touch pad

control panel with two pushbuttons from which all functions can be accessed.

These instruments are easy to adjust and maintain, with user replaceable batteries and

diffusion sensors.

INSTRUMENT TYPE GAS DETECTED RANGE

OX-94 Oxygen 0-40% volume

CO-94 Carbon Monoxide 0-500 ppm

HS-94 Hydrogen Sulfide 0-199.0 ppm

COMPONENTS AND CONTROLS

CASE

The 94 Series has a rigid plastic case that is durable and shock resistant. The sensor is

housed within the case, and faces upward. The display and touch pad control panel are

located on the side of the unit. The carrying case covers the entire unit, except it has a

hole for the sensor to protrude through and is also shaped so that it does not muffle the

audible buzzer sound. The plastic case has a substantial spring loaded clip for easy,

secure attachment to ones shirt pocket or belt.

SENSOR

The sensor is mounted within the plastic case on the top of the instrument. A water

resistant disc covers the sensor area, and is held in place with a rubber cap. This cap and

disc should be left in place for maximum water resistance. The sensor is inside the

instrument and is removable if the instrument is opened. The sensor plugs into sockets

on the PCB, for quick periodic replacement. The sensor principles of operation are as

follows:

Oxygen Sensor

The oxygen sensor is an electrochemical cell, consisting of gold and lead electrodes

in an alkaline electrolyte. A fluorocarbon membrane covers the cell, and allows

atmosphere to diffuse into the electrolyte at a rate proportional to the partial

pressure of oxygen. The oxygen reacts in the cell, producing a current proportional

to the concentration of oxygen. The current develops a voltage across a

temperature-compensating thermistor/resistor network. The voltage is measured

by the circuitry of the GX-82 and converted to a measurement of gas concentration.

CO & H2S Sensors

The CO and H2S sensors are electrochemical cells, consisting of three precious metal

electrodes in an acid electrolyte. A gas permeable membrane covers the cell, and

allows gas in the atmosphere to diffuse into the electrolyte at a rate proportional to

its partial pressure. The gas reacts in the cell, producing a current proportional to the

concentration of gas. The current is amplified by the circuitry of the 94 series

instrument and converted to a measurement of gas concentration.

CONTROL PANEL

The control panel is on the side of the instrument for easy access when the display is

viewed. It contains the display and switches that control the many functions of the

instrument. The switches are touch-pads, to reduce the possibility of accidental

activation or damage.

• POWER / MODE Button

The POWER / MODE switch controls power to the instrument, and is also

used for selecting the mode of operation of the unit.

• AIR Button

The AIR switch is used for adjusting the unit in fresh air, and is also used in

conjunction with the POWER / MODE switch for accessing various other

functions which will be explained later in this manual.

BATTERY COMPARTMENT

The 94 series battery compartment is located on the rear of the instrument. The sliding

access panel allows for easy replacement of the batteries. A large screw on the side of

the unit holds the battery compartment cover in place. The screw can be removed with

a screwdriver, fingernail, or coin.

The 94 series uses two “AAA” size cells standard alkaline batteries which will run the

unit for approximately 100 hours.

CIRCUIT BOARDS

The GX-82 has two circuit boards; the main board, and the sensor/buzzer board. The

main board contains the electronics and the display. The sensor/buzzer board contains

only the sensor and buzzer, and connects to the main board with a ribbon cable.

OPERATION

1. Start Up

A. Press and hold the POWER switch for two seconds. The buzzer will sound a

single tone, and the display will activate all of its digits and symbols.

B. After about 3 more seconds, the display will show a picture of a battery, and the

current battery voltage. A fully charged battery set will display 3 small blocks in

the battery symbol, and a low battery will display only one or two small blocks.

A dead battery will display no small blocks within the battery symbol.For best

results, replace the batteries when only one small block shows.

C. After another 3 seconds, the display will show the current gas concentration in

the surrounding atmosphere, in either ppm (H2S or CO), or in % volume

(Oxygen). The instrument will sound a double tone to indicate that it is now

warmed up and ready for operation.

2. Verify Operation

To easily verify operation of the OX-94, breathe out over the diffusion sensor on the

top of the instrument. The oxygen reading should drop to about 18%, the audible

alarm for Oxygen deficiency should sound, and the display reading should blink.

Press the POWER / MODE button to reset the alarm.

To verify operation of a toxic sensor on the HS-94 or CO-94, it is necessary to expose

the detector to a concentration of the gas to be detected (H2S or CO). Test gas kits

are available from RKI Instruments, Inc.

WARNING

If the Instrument does not respond to these verifications, take it to a known

“fresh-air” environment, then follow the zero and calibration procedures in

this manual. Repeat the Verify Operation procedure before using the

Instrument in a potentially hazardous location.

3. Normal Operation

The 94 Series Instrument will continuously monitor the atmosphere, display the O2,

H2S, or CO concentrations present, and sound alarm if a dangerous level is

encountered.

A. Backlight

The instrument has a display backlight to enable reading in dark areas. The

display backlight can be turned on by pressing the Mode button once, and it will

automatically turn off after 20 seconds. The backlight also automatically comes

on anytime any alarm condition occurs, except for low battery alarm.

B. Checking battery voltage

The battery voltage is displayed when the instrument is first turned on, as

described in section 1. B. above. A single tone will sound and the battery voltage

will show on the display. New alkaline batteries will register approximately 3.0V.

The minimum voltage required for operation is 2.1V. As the batteries get used

up, the small blocks within the larger battery outline on the display disappear as

follows:

2.3 volts or higher All three small blocks are present.

2.2 volts Two small blocks are present, indicating 10 to 20 hours of

battery life left.

2.1 volts Only one small block present, indicating less than 10

hours of operation left. It is recommended that the

batteries be changed when they reach this stage.

2.0 volts or lower No small blocks are present. The large battery outline

will blink off and on, and the instrument will sound a

constant tone alarm indicating that the battery is dead.

The battery voltage is now too low to properly operate

the instrument and the batteries must be replaced before

the instrument can be used.

Note

The 94 series automatically checks battery voltage during start-up; if the measurement

is below 2.1V, the instrument will not operate. During normal operation, when the

battery voltage drops to 2.0V, the battery sign will blink on the display, a continuous

alarm tone will sound, and the display will show a blinking battery.

WARNING

The instrument does not monitor the atmosphere during a dead battery alarm. When

the low battery indicator flashes on the display, take the instrument to a non-

hazardous location to change the batteries. (See Maintenance-Batteries.)

C. Peak (Minimum) Hold Function.

Press the Mode switch twice to enter this mode. During use,the instrument

automatically latches onto the maximum gas reading for the toxic gases (and

onto the lowest reading for the Oxygen version). This reading is displayed on the

readout, and can be reset once the actual gas condition has cleared by pressing

the MODE switch once. The PEAK HOLD function will activate itself for any

alarm condition, and can be reset once the gas condition is below the alarm level

(or above the alarm level for the Oxygen version). To clear the peak (or

minimum) readings, press the mode switch once after the gas condition has

cleared.

D. Toxic Gas (H2S and CO) Exposure.

Press the MODE switch three times to display the TWA value (time weighted

average dose for the last 8 hours of operation of the instrument).

Press the MODE switch four times to display the STEL value (time weighted

average dose for the last 20 minutes of operation of the instrument).

The instrument will return to normal operation itself after 20 seconds of

displaying these modes. To bypass the 20 second delay, press the MODE switch

to return to normal operation immediately.

4.Auto Zero/Span

To automatically adjust the zero point for H2S or CO, (or the span to 20.9% for

oxygen), take the instrument to a known fresh-air environment. With instrument in

normal operation, press and hold the AIR button. The unit will beep three times,

and then give a double beep indicating that it has adjusted to the surrounding

atmosphere.

5. Alarms

Gas Level Alarms

The 94 Series instruments have standard alarm points as listed below:

OX-94 19.5% decreasing, 23.5% increasing

CO-94 25 ppm increasing, 25 ppm TWA, 400 PPM STEL

HS-94 10 ppm increasing, 10 ppm TWA, 15 ppm STEL

When an alarm point is exceeded, the instrument sounds a pulsed tone, and the

display reading will blink. In the case of TWA or STEL alarms, the display will also

indicate which alarm level has been exceeded. The instrument reading will

automatically latch onto the highest reading (or lowest reading for low oxygen

levels). To reset, press the MODE switch once. If the gas concentration has dropped

to below the alarm point, the alarm will silence, and the unit will give the current

reading. If the unit has not dropped to below the alarm point when the MODE

switch is pressed, then the audible alarm will still sound and the unit will latch onto

the new reading present at the time the MODE switch was pressed.

Safety Self-Check

The 94 Series instruments continuously monitor themselves for proper operation. If

a malfunction occurs, a steady “trouble” tone will sound. There are two modes of

malfunction that will sound a steady

“TROUBLE” alarm. These are:

LOW BATTERY This alarm will sound if the batteries are too low

to operate the instrument. Replace the batteries

before further use.

SENSOR FAIL This alarm will sound if the sensor is missing or

has an internal open connection. This type of

alarm is indicated by the steady audible tone,

and with a large “X” appearing on the display

upper left. To resolve, verify that there is a sensor

in the instrument, or, replace the sensor if

necessary.

CALIBRATION AND MAINTENANCE

The 94 series microprocessor circuit allow the instrument to be calibrated and zeroed

completely with the external buttons. There are no internal user adjustments.

Note

Adjust the instrument Zero (or oxygen span at 20.9 %) if a gas reading drifts off zero

(or 20.9 %) or when a sensor has been replaced. All calibration and Zero adjustments

should be done in a known clean air environment.

Calibration Supplies and Equipment

To adjust the 94 series monitors, you will need the appropriate calibration gases and

supplies.These are readily available from RKI in an RKI Calibration Kit. The kits contain

calibration gas, valve, test cup, tubing, and any other accessories necessary. Although

other concentrations could be used, the recommended calibration gas concentrations

are as follows:

HS-94 25 ppm H2S in nitrogen or in air.

CO-94 50 ppm CO in nitrogen or in air.

OX-94 100 % nitrogen.

Entering Calibration Mode:

To access calibration mode on the 94 series instruments, the unit must be initially turned

on a special way. Turn the instrument OFF and turn back on as follows:

1. Press and hold the AIR button.

2. While continuing to hold the AIR Button, press also the MODE button until

instrument beeps.

3. After the beep, release the MODE button but continue to hold the AIR button

for a few seconds until the display completes warmup and reads the gas

concentration. Just to the left of the gas reading there will be a small arrow

pointing downward. This indicates that the instrument is ready to set the zero

reading.

Zeroing the instrument:

4. Apply the zero gas. For the H2S or CO units, the Zero gas can be the

surrounding ambient air if it is known to be gas free. For the Oxygen version,

expose the sensor to a known oxygen free sample such as 100% nitrogen. Flow

the gas onto the sensor using a test cup covering the sensor area on the top of

the unit, and allow sufficient time for the reading to stabilize, typically 30 to 60

seconds. If you wish to skip the zero adjustment, press the MODE switch and

continue to step 7.

5. Once full reading is reached, press the AIR button for about 5 seconds. The unit

will beep 3 times initially, and then two more times to indicate that it has

completed the adjustment.

Calibrating the instrument:

6. Press the MODE switch one time. The small arrow on the display to the left of

the gas reading will change to pointing upward, indicating that the instrument is

now in the “span set” mode.

7. For H2S or CO units, go to step 8. For Oxygen units, take the instrument to fresh

air, press and hold the AIR button until the unit has beeped 5 times. The last 2

quick beeps indicate that the unit has completed the calibration adjustment. Now

press the mode switch once to return to normal operation.

8. For H2S and CO units, after step 6 above, the display will read a value that the

instrument believes is the concentration of the calibration gas that will be

applied. If the value displayed matches the value of the calibration gas that you

will apply, then go to step 9. If it does not match, then press the AIR button to

scroll the reading to the correct value of your calibration gas. Note that the

readout will only scroll up, but will return to Zero and start over after it reaches

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