2 Overview
US SENTRY io 13
2.3.4 Gas Reading Conversion
Combustible, toxic, and oxygen gas readings use the following equation:
Gas Reading = [(Io-4)/16] * DU * DP
DU: Display Units
DP: Decimal Positon - Resolution of the gas reading
2.3.5 Faults
The Sentry io displays a general sensor fault when the gas detector analog value dips into fault condition. This fault is
shown on the home screen and in the alarm log with a time stamp.
For MSA’s HART enabled detectors, certain fault codes are shown in the Sentry io diagnostics tab for the detector. These
fault codes should be referenced against the MSA instrument's instruction manual for the relevant fault code explanation.
The Sentry io also shows a general fault if there is an internal error or PLC failure.This fault is shown on the home screen
and in the alarm log with a time stamp.
2.4 Power Source Compatibility and Budgeting
2.4.1 Power Compatibility
SENTRY io is available with a factory-installed 24 VDC power supply compatible with main power sources as described in
7 Technical Specifications.
Ensure your system does not exceed rated total current output capacity of the 24 VDC power supply.
2.4.2 Power Budgeting—Connected Field Device Power Allocation Calculation
The SENTRY io internal power supply is provided to enable powering 24 VDC field input and output devices connected to
the panel. The SENTRY io internal modules will consume a certain portion of the available amperage. In all cases, the user
must ensure the total amperage load of all connected input and output devices do not exceed the remaining amperage
capacity of the SENTRY io power supply.
Calculate total power requirements of all connected analog signal input devices and total 24 VDC power load of all
connected output devices from cold start. The sum total power draw of all connected input and output devices must not
exceed unallocated, available amperes of available 24 VDC power. Use the power consumption worksheet in the SENTRY
io Online Help to calculate the power load requirements and available budget for field devices.
NOTE: If the SENTRY io relay output contacts will be switching DC or AC power supplied from an external source, these
power loads will not be included in your calculation.
2.5 Installation Recommendations
For SENTRY io installation, MSA recommends the following:
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Only located in areas that comply with SENTRY io specifications. See 7 Technical Specifications.
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Located in areas that allow for easy access to the touch screen and internal components as necessary to configure,
view, and service.
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Access to open the door
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Access to power source, breaker, etc.
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Access to field cabling trays/exit points—select location with consideration to wiring routes
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Out of direct sunlight
NOTE: The SENTRY io internal temperature can depend on system electrical load as well as thermal loading from
direct sunlight. It is best to not mount in direct sunlight or near other excessive heat sources.
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