Model 5100-28-IT Combustible Gas Sensor Module
cable shield must never be used as a conductor. Larger gauge wire is recommended with distances over
1000’. Connect wires as shown in figure 4-4.
For a 4-Wire isolated connection, set jumpers, located on the bottom of the transmitter board, to the upper
position as illustrated in Figure x.x. Verify that both jumpers are in the position marked by 4-wire. When
using a 4-wire connection, a minimum of 2 each of an 18 AWG, 2 conductor twisted/shielded pair cable
must be used. A cable shield must never be used as a conductor. Larger gauge wire is recommended
with distances over 1000’. Connect wires as shown in figure 4-4.
4.2.2 MODBUS OPERATION USING RS-485 CONNECTION
Use a minimum of 18 AWG, 2 conductor for DC power connection. No shield required. In addition use a
minimum of 24 AWG, low capacitance, shielded data cable for RS485 half duplex communication. The
installation may be planned in a manner which provides up to 32 sensor modules on a single home run.
TERMINATION RESISTOR JUMPERS:
Termination resistors are used in RS-485 wire runs to provide impedance matching. The IT series
modules use a 120 Ohm resistor for this function. The cable being used for this RS-485 connection must
have a minimum of 100 Ohm impedance with a maximum of 120 Ohms.
Installations where the cable length is under 100’, termination resistors may not be required. In
installations where the cable length is greater than 100’, it is recommended to place the termination
jumpers on the first device and last device on the RS-485 wire run. Termination jumpers must be removed
from all other modules connected between the first and last device. The first device in the RS-485
multiplexed bus is usually a gas controller or PLC. Factory term resistor setting is “not enabled.”
BIAS JUMPERS: (BIAS A, BIAS B)
Bias resistors are used to force RS-485 receiver outputs to a known (fail-safe) state, when the bus is idle.
Bias jumpers are always installed in pairs as the bias must be placed on both the TX A and TX B lines.
Sierra Monitor’s IT series of combustible gas sensors automatically apply the bias jumpers, and are factory
installed so that the bias is always enabled.
4.2.3 SENTRY OPERATION USING SENTRY PSG CONNECTION
Use a minimum of 18 AWG, 3-conductor cable up to 2000’. The cable may or may not be shielded. We
recommend shielded cable in circumstances that there could be RF or EM interference present. Shield to
be terminated and grounded only at the Sentry controller. Shield must be cut and dressed at the module
end so that no part of it comes in contact with the conduit or ground.
Be sure to follow all local electric code and safety requirements when installing the 5100-28-IT Gas Sensor Module
Install conduit as required by local code or construction specifications. Provide for splice boxes where
multiple modules will be wired to a single run. Pull conductors of the correct gauge wire from the controller
to each splice box and from the respective splice box to each planned module location. See for proper
wire termination in the splice box. Twisted wire secured with wire nuts is not an acceptable splice.
RFI Noise Suppressor must be added to power/ground as per Appendix D.
The drain wire of shielded cable must NOT be used as one of the conductors.
Installation and wiring must be in accordance with the National Electrical Code. Temperature
rating of cable wire must be at least 75oC. If cable runs through higher temperature
environments, it must be specified for that environment.
4.3 ENCLOSURE INSTALLATION
To protect the transmitter and sensor assembly they should be removed from the enclosure and preserved
until final installation and wiring termination.