RKI Instruments 35-3000RKA-LEL User Manual

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35-3000RKA-LEL Sample Draw Combustible Gas
Detector

Specifications

Table 1 lists specifications for the sample draw combustible gas detector.

Table 1: Specifications

Target Gas Combustible Gas
Input Power 24 VDC
Construction (housing) Fiberglass/polyester (NEMA 4X)
Dimensions 8.5 in. H x 6.5 in. W x 4.25 in. D
Weight 4.5 lbs.
Sampling Method sample draw
Sample Flow 1.5 SCFH (nominal)
Detection Range 0 to 100% LEL
Response Time 90% in 30 seconds
Linearity
Repeatability

5% of detection range
2% of detection range

Sample Draw Combustible Gas Detector • 1

O

Description

This section describes the components of the sample draw combustible gas detector. The
sample draw detector consists of the housing, flow system, and detection system.

Mounting

Flow Adjust
Potentiometer

Pu mp /flo w sw itch
terminal block

Fail LED

Pilot LED

Flowmeter

Bypass valve
Particle filter

LE L Transmitter

Foot, 4X

Flow Alarm Setpoint
Adjustment Potentiometer

Se nso r Wiring
Terminal St rip

External Wiring
Terminal Strip

Exhaust

Inlet

Factory Set Pots

Test Points
100 - 500 mV range

JUMPER PINS FOR
FACTORY U SE ONLY

Span Pot

Zero Pot

Housing

The sample draw detector’s fiberglass housing is weather- and corrosion-resistant. It is
suitable for installation where general purpose equipment is in use.

LEL
sensor

P/N 57-1050RK

REV. 0

GND

24V

TP +

4-20

POWER/SIG

RED

WHT

SENSOR

GRN

BLK

ZER

SPAN

TP

Terminal Block

3/4" Conduit
Hub, 2X

Figure 1: Sample draw Combustible Gas Detector Component Location

The housing door is hinged on the left side and is secured by two latches on the right side.
The flowmeter and status lights are visible through a window in the housing door.

Four mounting feet are attached to the back of the housing (one at each corner). Use the
mounting feet to install the housing to a vertical surface. Use the two conduit hubs on the
bottom of the housing to make wiring connections.

An aluminum subpanel is mounted to the interior of the housing. The sample draw
detector’s internal components are mounted to the subpanel.

2 • Sample Draw Combustible Gas Detector

Flow System

The sample draw detector’s flow system consists of the INLET fitting, filter, pump,
flowmeter, bypass valve, status lights, pressure switch, and EXHAUST fitting (see
Figure 1). Figure 2 illustrates how the gas sample moves through the flow system.

To

Exhaust

Bypass

Valve

Flowmeter

Inlet Filter Pump Sensor

Pressure Switch

Figure 2: Sample draw Combustible Gas Detector Flow Diagram

INLET fitting

The INLET fitting on the right side of the housing allows the gas sample to enter the
sample draw detector. The INLET fitting accepts 1/4 in. rigid tubing. See the Installation
section on page 7 to connect tubing to the INLET fitting.

Filter

The dust filter is below the main circuit board. The filter prevents particulates in the
incoming gas sample from damaging the flow and detection systems. Replace the filter
when it appears dirty, discolored, or clogged.

Pump

The pump is behind the main circuit board near the top of the sample draw detector.
The pump pulls the gas sample into the sample draw detector. The pump operates on
24 VAC, which is generated from the 24 VDC supplied to the sample draw detector.

Flowmeter

The flowmeter is attached to the main circuit board near the top left corner (see Figure 1.)
You can see it through the window in the door. A ball in the flowmeter column indicates
the flow rate of the sample draw detector. The flowmeter measures the flow in the range

0.2 to 2.0 SCFH (Standard Cubic Feet per Hour). The optimum flow rate is 1.5 SCFH.

Bypass valve

The bypass valve is to the left of the flowmeter. The bypass valve adjusts the flow rate to
the sensor. Use a flat-blade screwdriver to adjust the bypass valve.

NOTE: The bypass valve allows fine adjustments of the flow rate. For a wider range of

adjustment, use the flow adjust potentiometer (see Figure 1.)

Sample Draw Combustible Gas Detector • 3

Status lights

Two status lights are above the flowmeter. They are also visible through the window in
the housing door.

Pilot light

The green Pilot light is on when the sample draw detector is receiving power.

Fail light

The red Fail light is on when the sample flow rate is below the low flow level.

NOTE: The default low flow level is 0.6 SCFH ( ± 0.2). See “Adjusting the Low Flow

Setting” on page 15 to adjust this setting.

Pressure switch

The pressure switch is mounted to the opposite side of the main circuit board. The
pressure switch monitors the flow rate of the incoming gas sample.

If the flow rate falls below the preset low flow level, the pressure switch causes the fail
relay to interrupt the signal in the 4-20 mA line. This causes a downscale reading at the
monitor. The low flow level is factory-set at 0.6 SCFH ( ± 0.2 SCFH).

EXHAUST fitting

The EXHAUST fitting on the right side of the housing allows the gas sample to exit the
sample draw detector. The EXHAUST fitting accepts 1/4 in. rigid tubing. See the
Installation section on page 7 to connect tubing to the EXHAUST fitting.

Detection System

The detection system consists of the combustible gas sensor, the hydrogen transmitter,
and the main circuit board.

Combustible gas sensor

The combustible gas sensor is installed in a cavity block. The cavity block is mounted to
the aluminum subpanel near the bottom of the sample draw detector. The combustible
gas sensor includes the sensing elements, flame arrestor, connector, and sensor leads.

NOTE: The cavity block includes a cavity for an oxygen sensor. This version of the

sample draw detector does not include the oxygen sensor.

Sensing elements

Two sensing elements are protected within the sensor assembly. Through a series of
thermal and electronic reactions, these elements produce an output that is pr oportional to
the detection range of the sample draw detector . The transmitter converts the output to a 4

- 20 mA signal which can be used by a recording or monitoring device.
The porous flame arrestor allows the gas sample to enter the sensor assembly and contact

the sensing element. The flame arrestor also contains sparks within the sensor.

4 • Sample Draw Combustible Gas Detector

Connector

The top of the sensor includes five pins that plug into the socket connector . This connector
allows you to replace the sensor without disconnecting the wiring. The sensor leads are
soldered to the connector.

Sensor leads

Four color-coded leads extend from the connector. The leads allow you to connect the
combustible gas sensor to the main circuit board.

Transmitter

The transmitter is mounted to the left of the combustible sensor. It consists of the span
pot, zero pot, transmitter interconnect terminal strip, sensor terminal strip and test points.

Span/zero pots

The span and zero pots are located at the bottom edge of the transmitter and are used for
calibration. Use the span pot to make adjustments to gas response readings and the zero
pot to make adjustments to the zero reading

Transmitter interconnect terminal strip

The transmitter interconnect terminal strip is the six-point terminal strip near the right
edge of the transmitter. The transmitter is factory wired to the sensor and main circuit
board.

Test points

The test points are located on the left side of the transmitter and are labeled TP+ and TP- .
A 100 mV - 500 mV output is available at these testpoints for use during calibration.

Main Circuit Board

The main circuit board includes the interconnect terminal strip, transmitter terminal strip,
pump terminal strip, and relay (see Figure 1).

NOTE: The flowmeter and status lights are mounted to the main circuit board but are

considered part of the flow system.

Interconnect terminal strip

The interconnect terminal strip is the nine-point terminal strip near the bottom edge of the
main circuit board. Use the interconnect terminal strip to connect the sample draw
detector to power and external devices.

Transmitter terminal strip

The transmitter terminal strip is the nine-point terminal strip near the right edge of the
circuit board. Use the transmitter terminal strip to connect the transmitter to the main
circuit board.

NOTE: The transmitter is factory-wired to the circuit board. See the “Installation” section

on page 7 for all wiring procedures related to the sample draw detector.

Sample Draw Combustible Gas Detector • 5

Pump terminal strip

The pump terminal strip is the four-point terminal strip near the top edge of the circuit
board. Use the pump terminal strip to connect the pump and pressure switch to the main
circuit board.

NOTE: The pump and pressure switch are factory-wired to the circuit board. See the

“Installation” on page 7 for all wiring procedures related to the sample draw
detector.

Relay

The relay is to the left of the detector terminal strip. The relay is single-pole, double-throw
(SPDT) and is rated for 2 amps at 25 VDC (resistive). If the pressure switch senses a low
flow condition, the relay interrupts the signal from the transmitter. The interrupted
transmitter signal causes a fail condition at the Pioneer.

6 • Sample Draw Combustible Gas Detector