GMI D1033D User Manual

Technology for safety
12
D1000 series - Intrinsically Safe Isolators
All electronic equipment operate using electrical power and dissipate part of it into heat which is generally removed by the surrounding ambient air
and determines an increase in the operating temperature. High operating temperatures reduce their life and increase the probability of failures
according to the Arrhenius criteria, for example an operating temperature increase from 25 to 50 °C can cause a failure rate ten times higher.
In a cabinet air circulates and removes heat by convection (natural convection cooling) or, more effectively, by forced ventilation (fans) or even
more effectively by refrigerated forced ventilation (air conditioning). Installation of electronics in cabinets restricts free air movement and rises their
internal temperature. These effects can be reduced in two concurring lines of action:
by limiting the power dissipation and the heat produced inside the cabinet
by encouraging air circulation (and exchange of heat) inside the cabinet
A simple way to improve air circulation is to provide space between the isolators, also installing isolators in horizontally oriented DIN rail rows with
the enclosure main surfaces oriented vertically allows better air circulation inside the enclosure and significantly improves heat exchange.
What ultimately determines the operating temperature rise inside a cabinet is the total power dissipation and the provisions available for removing
the heat with cool air (natural convection or forced cooling). The maximum power consumption of each type of isolator is specified in the
corresponding data sheet so by summing the power of each unit in the cabinet the total power Pmax can be easily found. In normal operating
conditions however the power dissipated by the installed equipments is not likely to be the maximum value specified for all of them and at the
same time, the value of the effective power Peff can therefore be considered smaller (typical 70 %) than the value Pmax:
Peff ≤ Σ Pmax * 70 %
1) Closed Cabinets with Natural Convection
Closed cabinets are preferred in dusty or harsh environments where they offer a better equipment protection but their heat / power dissipation
capability is modest. Heat is removed by air flowing internally and exchanged with the walls of the cabinet, the calculation of the maximum allowed
power dissipation in this type of cabinet is:
Pmax = Δt * S * K and Δt =
———
where: Pmax [W] maximum allowed power dissipation
Δt [°C] maximum allowed temperature rise
S [m²] free heat emitting surface of the cabinet
K [W/m² * °C] thermal conductivity coefficient (K=5.5 for painted steel sheets)
As an example a cabinet sized 600x600 mm and 2000 mm high has a temperature rise of 10 °C for an installed power of 250 W.
2) Open Cabinets with Natural Convection
Open cabinets must operate in clean environments, their heat / power dissipation capability is medium.
Heat is removed by air flowing through the equipment, circulating from bottom to top of cabinet (convection). Depending on the type of engineering
(freedom of cool air to enter at the bottom of the cabinet, to circulate vertically around the equipment extracting heat and to exit at the top of the
cabinet), the power dissipation improvement can be two times better than case 1.
The cabinet must be equipped with inlet and outlet louvers in the lower and upper ends of the cabinets, vertical air flow inside and outside the
cabinet must be kept free from obstacles to enhance the “chimney effect” air circulation.
As an example a cabinet sized 600x600 mm and 2000 mm high has a temperature rise of 10 °C for an installed power of 350 W.
3) Open Cabinets with Forced Ventilation
Open cabinets must operate in clean environments, their heat / power dissipation capability is high with forced ventilation Air is forced into the
louvers on the bottom of cabinet, flows through the equipments, and finally exits at the top of the cabinet, where generally is forced by one or more
fans. The calculation of the required airflow is:
Q = 3.1 * Peff / Δt
where: Q [m³/h] is the required air flow
Peff [W] is the dissipated power (typical 70 % of the maximum power dissipation)
Δt [°C] is the maximum allowed temperature rise in the cabinet
As an example a cabinet sized 600x600 mm and 2000 mm high has a temperature rise of 10 °C for an installed power of 500 W.
4) Closed Cabinets with Forced Ventilation and Heat Exchanger
Closed cabinets with forced ventilation are preferred in high dissipated power and harsh environment where natural convention cabinets cannot be
used. Hot air is extracted from the cabinet by a fan, cooled by a heat exchanger (using a cooling fan with ambient air) and forced back into the
cabinet; depending on the type of engineering the improvement can reach a 5 times higher power dissipation than in case 1.
As an example a cabinet sized 600x600 mm and 2000 mm high has a temperature rise of 10 °C for an installed power of 1000 W.
Installation of Electronic Equipments in cabinet
P
S * K

GMI D1033D Specifications

General

Brand	GMI
Model	D1033D
Category	Switch
Language	English