EMS Guardian vs. WatchDog 800: Which Is Right for Your Application?

The EMS Guardian and WatchDog 800 use a single-pass optical arrangement to detect changes in light transmitted across a stack or duct. Their main differences are the information they provide and how that information connects to your equipment.

The EMS Guardian is a smoke-opacity detector that activates relay contacts at a selected alarm level. The WatchDog 800 is a continuous opacity monitor that displays opacity readings and provides a recordable 4–20 mA signal for percent opacity.

Both are backed by Environmental Monitor Service, a certified veteran-owned small business manufacturing and servicing opacity monitors since 1990.

Compare the Features

Feature	EMS Guardian	EMS WatchDog 800
Primary purpose	Smoke-opacity detection and alarm control	Continuous opacity measurement, display and process-control output
Optical arrangement	Single pass	Single pass
Light source	Electronically modulated green LED	Electronically modulated green LED
Optical path length	2–8 feet	3–8 feet
Operator information	Status indicators and selectable smoke-opacity alarm threshold	Digital display of measured opacity with push-button controls
Alarm settings	Approximately 5%, 10%, 15% or 20% opacity	Adjustable from 1% to 75% opacity
Alarm relays	Two instantaneous relays	One instantaneous alarm relay
Analog output	Relay-based alarm signaling	One recordable 4–20 mA analog output for percent opacity
Calibration features	Push-button digital calibration and window-dust compensation	Clear-path zero adjustment, span adjustment using a neutral-density filter, and checks with additional filters
System power	12 VDC power supply	24 VDC power supply

When Should You Consider the EMS Guardian?

Consider the EMS Guardian when your equipment needs a straightforward smoke-opacity alarm that activates relay contacts at a selected threshold.

For crematory smoke detection and incinerator applications, the Guardian can provide an alarm signal when smoke opacity exceeds the configured level. Its two instantaneous relays remain active until opacity falls below the set point.

The Guardian may be a suitable choice when:

• Your equipment needs a relay signal when smoke opacity exceeds a selected limit.
• A continuous numerical opacity display and analog signal are not required.
• You are replacing an older smoke detector and want EMS to review the existing mounting ports and controls.

View the EMS Guardian Smoke Opacity Detector

When Should You Consider the WatchDog 800?

Consider the WatchDog 800 when you need continuous opacity readings, a local digital display and a recordable 4–20 mA signal for connection to compatible plant controls or recording equipment.

For operators selecting a crematory opacity monitor or commercial boiler opacity monitor, the WatchDog 800 provides measurement information that helps them follow changes in exhaust conditions. Its adjustable alarm relay also provides a signal when opacity exceeds the selected threshold.

Applications include:

• Crematories and incinerators
• Commercial boilers and combustion furnaces
• Baghouses and dust-collection systems
• Commercial exhaust and duct systems
• Fan-control and other industrial process-monitoring applications

View the EMS WatchDog 800

Choosing a Crematory Smoke Monitor

Start with the information your cremation equipment requires. Does the controller need an alarm contact when smoke exceeds a threshold, or does it need a continuous opacity signal?

The Guardian suits applications centered on smoke detection and relay response. The WatchDog 800 adds continuous opacity monitoring, a numerical opacity display and a recordable analog measurement signal for percent opacity.

EMS can help manufacturers and end users review the stack dimensions, mounting arrangement, equipment controls and monitoring requirements before choosing a system.

Where an application specifically requires EPA Performance Specification 1 monitoring, review the EMS WatchDog PS-1 and our EPA PS-1 requirements guide.

Installation, Maintenance and Support

Both systems need proper optical alignment and access for inspection and cleaning. Follow the applicable manual for setup, calibration and maintenance procedures.

EMS provides application assistance, replacement parts, troubleshooting and repair support throughout the life of your equipment.

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