Murco MGS Provozní pokyny stáhnout pdf (Strana 2)

1- MGS Installation Instructions

To open the Standard Sensor enclosure: turn the cable gland ½ turn

anticlockwise to loosen the internal gland nut, depress the clip on top of the

enclosure and open. Reverse to close.

Power: 12-24V AC / DC, connect at positions 0V and +V at connector block

CN1. For AC – Jumper A is on, D is off. (See Diagram 1/2)

For DC – Jumper A is off, D is on. (Default Factory Setting is DC)

Use 2 cores of a 4-core cable, low voltage alarm type, typically 7/0.2

mm sq

Output: you can select the V or mA analogue output at JP1 and JP3. (Default

factory setting is mA) Connect the other two cores of the cable to terminal

block CN2 positions 0V and V or I for voltage or current as per jumper

selection. You can common the two zeros and use 3 core cable if preferred.

connect 4-20mA at CN 2 positions 0V and I

connect voltage output at CN 2 positions 0V and V

Relay set point: P1 sets the trip point for the relay and sounder using the 0-

5V scale (measure at test points 0V and REF1, 2.5V would be equivalent to

half the range - (500ppm on a scale of 0-1000ppm) Default factory setting is

50% of the range.

Time delay: A time delay for the operation of the relay and sounder can be

selected using jumpers JP5 and JP6. Default factory setting is zero.

Sounder: The sounder can be disabled using jumper JP2. Default factory

setting is enabled.

There is a 5-minute power up delay to allow the sensor to stabilize. This can

be cancelled by momentarily shorting between either of the upper and lower

pads of SW1 or SW2.

2- MGS - Location Instructions

Location of Sensors

Sensors must be located within the appropriate wire lengths from the central

control unit (if used).

In all cases the sensor supplied is designed for maximum sensitivity to a

particular gas.

However, in certain circumstances false alarms may be caused by the

occasional presence of sufficiently high concentrations of other gaseous

impurities. If such a situation is likely to arise installers should check with our

Technical Department so that sensor (s) of suitable cross sensitivity can be

supplied. Examples of situations where such abnormalities may arise include.

• Plant room maintenance activity involving solvent or paint fumes or

refrigerant leaks.

• Plant rooms in fruit ripening/storage facilities because of accidental gas

migration (bananas - ethylene, apples - carbon dioxide)

• Heavy localised exhaust fumes (carbon monoxide, dioxide, propane)

from engine driven forklifts in confined spaces or close to sensors.

A response delay may be selected to minimise any problems that might arise.

Machinery rooms

There is NO ABSOLUTE RULE in determining the number of sensors and their

location. However a number of simple guidelines will help to make a decision.

Sensors monitor a point as opposed to an area. If the gas leak does not reach the

sensor then no alarm will be raised. Therefore, it is extremely important to

carefully select the sensor location. Also consider ease of access for maintenance.

The size and nature of the site will help to decide which method is the most

appropriate to use. Locations requiring the most protection in a machinery or

plant room would be around compressors, pressurised storage vessels,

refrigerant cylinders or storage rooms or pipelines. Most vulnerable are valves,

gauges, flanges, joints (brazed or mechanical), filling or draining connections etc

When mechanical or natural ventilation is present mount a sensor in the airflow.

In machinery rooms where there is no discernable or strong airflow then

options are:

• Point Detection, where sensors are located as near as possible to the

most likely sources of leakage, such as the compressor, expansion

valves, mechanical joints or cable duct trenches, and,

• Perimeter Detection, where sensors completely surround the area or

equipment.

• With heavier than air gases such as halocarbon and hydrocarbon

refrigerants such as R404A, propane, and butane sensors should be

located near ground level

• With lighter than air gas e.g. ammonia, the sensor needs to be located

above the equipment to be monitored on a bracket or high on a wall

within 300 mm of, or on the ceiling provided there is no possibility of a

thermal layer trapped under the ceiling preventing gas reaching the

sensor. (NB. At very low temperatures, such as in a refrigerated cold

store, ammonia gas becomes heavier than air).

• With similar density or miscible gases, such as CO or CO2, sensors

should be mounted about head high – say 1.5m.

• Sensors should be positioned a little way back from any high-pressure

parts to allow gas clouds to form. Otherwise any leakage of gas is likely

to pass by in a high-speed jet and not be detected by the sensor.

• Make sure that pits, stairwells and trenches are monitored since they

may fill with stagnant pockets of gas.

• If a pressure relief vent pipe is fitted to the system, it may be a

requirement to mount a sensor to monitor this vent pipe. It should be

positioned about 2 m above the PRV to allow gas clouds to form.

• With racks or chillers pre-fitted with refrigerant sensors, these should be

mounted so as to monitor the compressors or if extract ducts are fitted

the airflow in the duct may be monitored.

Refrigerated Spaces

In refrigerated spaces sensors should be located in the return airflow to the

evaporators on a sidewall, below head high preferred, or on the ceiling, not

directly in front of an evaporator. In large rooms with multiple evaporators,

sensors should be mounted on the central line between 2 adjacent

evaporators, as turbulence will result in airflows mixing.

Chillers

In the case or small water or air-cooled enclosed chiller units mount the

sensor so as to monitor airflow to the extract fans. With larger models also

place a sensor inside the enclosure under or adjacent to the compressors

In the case of outdoor units:

• such as enclosed air-cooled chillers or the outdoor unit for VRV/VRF

systems mount the sensor so as to monitor airflow to the extract fan.

With large units also place a sensor inside the enclosure under or

adjacent to the compressors

In the case of non-enclosed outdoor units

• If there is an enclosed machinery section then locate a sensor there.

• In the case of units with enclosed compressors, mount sensors in the

enclosures

• Where you have protective or acoustic panels mount the sensor low

down under the compressors where it is protected by the panels.

• With air-cooled chillers or air-cooled condensers with non-enclosed

condenser sections it is difficult to effectively monitor leaks in the coil

sections. With some designs it will be possible using an airflow sensor

to monitor airflow to the start –up fans in the front or rear sections.

• If there is a possibility of refrigerant leaks into a duct or air-handling unit

install a sensor to monitor the airflow.

Weatherproof sensors should be used for unprotected outdoor applications.

Air Conditioning – Direct systems URV/URF

EN378 states that at least one detector shall be installed in each occupied

space being considered and the location of detectors shall be chosen in

relation to the refrigerant and they shall be located where the refrigerant from

the leak will collect. In this case refrigerants are heavier than air and detectors

should have their sensors mounted low .e.g. at less than bed height in the

case of an hotel or other similar Category Class A spaces. Ceiling or other

voids if not sealed are part of the occupied space.

In a hotel room monitoring in ceiling voids would not

strictly comply with EN378

Do’s Don’ts

••

mount the in-room sensor at less than the

normal heights of the occupants e.g in a

hotel room this is less than bed height -

between 200-500mm off the floor.

••

away from draughts and heat sources like

radiators etc.

••

avoid sources of steam

••

Do not mount sensors

– under mirrors

– at vanity units

– in or near bathrooms

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