INSTRUCTION MANUAL Model NP-204 PORTABLE METHANE GAS DETECTOR The accompanying instrument is sold and serviced in the USA by RKI Instruments, Inc. Please contact R KI Instrumentsfor any follow up service needs, including questions, warranty issues, repairs, and spare parts and sensors. Thank you for selecting this fine instrument for your use. With proper care and maintenance, it will provide you with many.
NP-204 RKI Instruments, Inc. Table of Contents INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 COMPONENTS AND CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case . . . . . . . . . . .
NP-204 RKI Instruments, Inc. INTRODUCTION The Model NP-204 is a proven gas detection instrument, in use internationally for detection of natural gas levels over the full range of concentrations. The NP-204 is compact, easy to use, and offers the following features: • Battery operated, the NP-204 can use either alkaline or Ni-Cad cells. Batteries are easily field replaceable. • The NP-204 detects natural gas over two ranges : 0-5% volume (or optionally 0100% LEL), and 0-100% volume.
NP-204 RKI Instruments, Inc. DESCRIPTION The RKI Model NP-204 is a rugged battery operated portable instrument for detection of combustible gas (methane) levels over a wide range.The two ranges, 0-5% by volume and 0-100% by volume, are displayed on a built in analog meter. The NP-204 utilizes a rubber aspirator bulb for drawing of a test sample through a hose and probe.
NP-204 RKI Instruments, Inc. 100% Volume Gas Sensor The Volume Percent Gas sensor also consists of a filament set and wires. The filaments are similar to the LEL sensors in that they are inserted and attached to the internal, flame arrestor protected flow chamber. The flow chamber brings the sample gas to the filaments when the aspirator bulb is squeezed. 100% Volume gas sensor - Principle of Operation The 100% Volume gas sensor is a Thermal Conductivity (TC) type of sensor.
NP-204 RKI Instruments, Inc. switch is in this position the instrument will detect and display the high range only. 2. ZERO ADJ. This adjustment is used to Zero the reading for the LOW range. This is generally done before each use of the instrument. (The zero adjustment for the % gas range only rarely needs adjustment, so is not externally adjustable). 3. VOLT ADJ. This adjustment is used to set the voltage for the detectors. When the “RANGE” switch is in the “Volt Adj.
NP-204 RKI Instruments, Inc. OPERATION Preparation Normally the NP-204 requires very little preparation before use. Before using the instrument, follow the steps listed below: Start-up 1. Mechanical Zero Before turning the instrument on, set it on a flat surface and verify that the meter reading is exactly on zero. If necessary, turn the Mechanical Zero adjustment to bring the reading to zero. The mechanical zero adjustment is located centered directly underneath the meter. 2.
NP-204 RKI Instruments, Inc. 5. Verify Response (Low Range) To verify detection of combustibles use a controlled source of flammable vapor, for example a bottle of isopropyl alcohol. For accurate testing of calibration, use a known calibrating gas source, such as 50% LEL methane. (See calibration section of this manual for calibrating instructions). After verifying response, squeeze the aspirator bulb 5 times again to flush fresh air through the system.
NP-204 RKI Instruments, Inc. Zero Adj. knob. 3. Generally, when testing an unknown space or sample, it is recommended to have the range selector switch in the H position. This helps to extend the life of the Low range sensor by not stressing it with exposures to very high concentrations. 4. Attach hose and probe and check for leaks by holding finger over probe inlet while squeezing aspirator bulb. Bulb should remain collapsed if there are no leaks in the system. 5.
NP-204 RKI Instruments, Inc. Calibration Supplies and Equipment To adjust the NP-204, you will need the following supplies and equipment, some of which is available in an RKI Calibration Kit: • Known calibrating sample of 2.5% Volume (50% LEL) natural gas (methane) in air. • A flowmeter with a range of 0 - 1.0 lpm (0-2.0 SCFH). • A control valve for the cylinder, and a tubing length to connect the gas to the NP-204. • A source of 100% natural gas or methane.
NP-204 RKI Instruments, Inc. Caution The combustibles measurement (low range) is flow-sensitive. Use a flowmeter and set the flow rate to 0.8 SCFH (0.4 l/m). 7. Remove the span gas tubing from the probe, and place the probe in fresh air. Squeeze the bulb 5 times to expose the sensor to fresh air, and then verify that the combustibles reading returns to zero. 8. Repeat the exposure to the calibrating sample and verify that the combustibles reading reaches the correct level.
NP-204 RKI Instruments, Inc. High Range sensor Replace the high range sensor filaments when: 1. The High range cannot be calibrated correctly. 2. The high range cannot be set to zero after warmup using the internal ZERO (H) potentiometer. Sensor Replacement 1. Take the NP-204 to a non-hazardous location and turn the power off. 2. Remove the instrument from the carrying case. 3.
NP-204 RKI Instruments, Inc. B. Remove the two screws holding the U shaped bracket which secures the TC sensor filaments into the sample chamber. Remove the bracket and pull the sensor filaments from the chamber. C. Install the replacement filaments into the chamber. Insure that the filaments with the black and white wires are installed into the hole closest to the corner of the instrument. Replace the U shaped bracket and tighten its two screws securely. D.
