Conducting a Site Survey (Gateway and Nodes)
A Site Survey, also known as a Radio Signal Strength Indication (RSSI), analyzes the radio communications link between the
Gateway and any Node within the network by analyzing the radio signal strength of received data packets and reporting the
number of missed packets that required a retry.
Perform a Site Survey before permanently installing the radio network to ensure reliable communication. Activate Site Survey mode
from either the Gateway buttons or the Gateway Modbus holding register 15. Only the Gateway can initiate a Site Survey, and the
Site Survey analyzes the radio communications link with one Node at a time.
Conduct a Site Survey Using the Menu System
Initiate a Site Survey using the Gateway’s buttons and menu system.
1. Remove the Gateway's rotary dial access cover.
2. Set the Gateway's rotary dials to the desired Node number.
For example, to check the status of Node 1, set the Gateway's left rotary dial to 0 and the right rotary dial to 1. To check
the status of Node 32, set the Gateway's left rotary dial to 3 and the right rotary dial to 2.
The Gateway is now enabled to read the status of the selected Node. The display scrolls through the Node’s I/O status.
3. Single-click button 1 to scroll across the menu levels until reaching the Site Survey (SITE) menu.
4. Single-click button 2 to enter the Site Survey menu.
5. Single-click button 2 to begin conducting a Site Survey with the Node selected in step 2.
The Gateway analyzes the quality of the signal from the selected Node by counting the number of data packets it receives
from the Node.
6. Examine reception readings (M, R, Y, G) of the Gateway at various locations.
Site survey results display as a percentage. M represents the percent of missed packets while R, Y, and G represent the
percent of received packets at a given signal strength.
M = Percent of missed packets; R = RED marginal signal; Y = YELLOW good signal; G = GREEN excellent signal. Record
the results if you need troubleshooting assistance from the factory.
7. Change the Gateway's rotary dials to conduct a Site Survey with another Node and repeat steps 2 through 6.
8. To end the Site Survey, double-click the Gateway's button 2.
9. Change the Gateway's rotary dials back to 0.
The LCD displays the device readings for the Gateway.
10. Double-click button 2 to move back to the top level menu.
11. Single-click button 1 to return to RUN mode.
12. Install the rotary dial access cover, referring to the Installation section of the manual to create an IP67 seal.
Interpreting the Site Survey Results
Site Survey results are listed as a percentage of data packets received and indicate the signal strength of the received signal.
Result
Description
Green
Packets received at a strong signal strength. A strong signal strength is greater than −90 dBm at
the receiver.
Yellow
Packets received at a good signal strength. A good signal is between −90 and −100 dBm at the
receiver.
Red
Packets received at a weak signal strength. A weak signal is less than −100 dBm at the receiver.
Missed
Packets not received on the first transmission and requiring a retry.
Judging if the reliability of a network’s signal meets the needs of the application is not just a matter of green, yellow, and red
packets received. In normal operating mode, when data packets are not received, the transmitter re-sends the packet until all data
is received.
For slow monitoring applications such as a tank farm, where data is required in terms of seconds or minutes, receiving most of the
data in the ‘red’ range, indicating a weak but reliable signal, transmits enough data for accurate monitoring. Nodes positioned near
the outside range of the radio signal may have 90% of the data packets received in the red zone, again indicating a weak, but
reliable signal.
We recommend keeping the missed packets average to less than 25%. When the network misses more than 25% of the data
packets, the signal is usually too unreliable or obstacles may be interfering with the signal. When Site Survey reports the missed
packets are 25% or higher, improve the radio system performance by:
•
Mounting the network’s antennas higher to clear obstacles in the area and improve the line of sight between Sure Cross
®
devices
Sure Cross
®
DX80 Gateway for Wireless Q45 Sensors
8
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