8
All low voltage connections should be completed before the
main power is connected to system.
All electrical connections must pass through a compression
gland. The glands can accept cabling from 11 to 21 mm in
diameter. After installation, the glands must be tightened to
ensure that the SSR-Ex maintains cabinet air pressure.
Mains power connects only to the Air Sentinel II.
No mains power should be connected directly to the main PCB.
Figure 11 - Low Voltage Connections
User Connections for SSR-Ex
RELAYS
4-20 mA
RMT CONNECTIONS
4.3.1 Low Voltage Connections
All of the low voltage electrical communication connections to the
instrument are made at the termination area located on the right side
of the main PCB. To access the connections, lower the access flap by
loosening the captive Phillips screws. The connections are labeled and
are self-descriptive. Please follow all government recommendations and
requirements for installation of electrical connections to and between
the instrument and other peripheral devices. All terminals are designed
to accept wires in the range of 14 - 28 AWG.
4.3.1.1 Relays
Two relay alarm connections labeled COM1, NC1 & NO1 and COM2,
NC2 & NO2 are provided. The relays are rated 240VAC 2A. Operation
of this alarm is covered in section 4.2.1.5 Alarms Menu.
4.3.1.2 4 - 20 mA Analog Output
These connections are located on the mid right side of the Main PCB.
The 4 - 20 mA output is driven by a 24 VDC power source and can
drive recorder loads up to 1000 ohms. Transformer isolation is provided
on the SSR-Ex. Operation of this output is covered in section 4.2.1.3 -
Analog Output Menu.
Polarities of the connections are labeled beside this termination on the
PC board.
The recommended cable is 22 AWG shielded twisted pair. To prevent
ground loops, connect the shield at its destination. The terminal block
is removable to assist in making connections.
The 4 - 20mA is factory calibrated. An adjustment is available on the
4 - 20mA in section 4.2.1.3 Analog Output Menu. In addition to making
adjustments, these menus output continuous 4 mA or 20 mA and
can be used as a signal test. The configuration mode will timeout
after 15 minutes.
4.3.1.3 Modbus
The RS-485 half-duplex (2-wire) digital interface operates with
differential levels that are not susceptible to electrical interferences.
Therefore, cable lengths up to 3000 ft can be implemented. The last
device on every bus may require a 120-ohm termination resistor to
eliminate the possibilities of signal reflection on the line. Do not run RS-
485 cables in the same conduit as power.
Ensure each instrument is not powered when connecting the RS-
485 line. To prevent damage to the instrument, ensure that power is
disconnected prior to making connections. The Modbus connection is
located on the lower right portion the main PCB as seen on Figure 11.
4.3.1.4 RMT
By design the SSR-Ex will only be actuated for measurement by a
remote command. The system can be set up to either be actuated
through MODBUS or by means of a remote actuation provided by the
end user.
These connections are located in the lower right corner of the main
PCB. See Figure 4 - Low Voltage Connections.
The instrument operates on user control software, where an external
control initiates each cycle. The SSR-Ex will indicate the current status
of connections using a relay contact that is closed when busy and
open when in standby mode.
4.3.1.5 Securing the Glands - Low Voltage
Low voltage connections to the instrument are made through electrical
glands located on the right side of the enclosure. Once the appropriate
low voltage wiring is inserted through the electrical gland and wiring
is secured at the terminals on the main circuit board glands on the
right side of the enclosure must be tightened to ensure wiring is
safely installed.
4.3.2 Mains Power Connections
Once all low voltage connections are made, the mains power should be
connected through the Air Sentinel II. Reference Figure 3 – Close-up of
Electrical Compartment.
4.3.2.1 Securing the Glands - Mains Power
Mains power connection to the instrument is made through an electrical
gland located on the left side of the enclosure. Once the mains power
wiring is inserted through the electrical gland and wiring is secured at
the mains power terminals of the Air Sentinel II electrical gland on the
left side of the enclosure must be tightened to ensure mains power
wiring is safely installed.
4.4 Hardware Control
The connections are labeled RMT Stby. The input has + and – polarity
connections and requires an external 24VDC control signal.
The output is simply a relay contact and is not polarized. After the
SSR-Ex completes a cycle of measurement, the unit will return to
standby awaiting another pulsed signal to measure. Alternately, 24VDC
can be continuously applied and the SSR-Ex will take readings until
the 24VDC is removed. When power is removed it will complete the
current cycle. The measured value will remain displayed until the
next measurement.
