FEATURES AND OPERATION
2-11
Part No. 001-4090-101/102
2.5.2.3 B+ Voltage
Current value of supply voltage. SWB+ is a 4-digit value in volts, e.g. a value of 13.3
indicates 13.3 VDC. This value should remain within the limits of 10-16 VDC ±2%.
2.5.2.4 Remote RSSI
Displays the strength of the last valid data signal received by a reporting remote unit. In a
polling type network, the last signal usually originates from the polling master unit. For the
master itself, the last signal received is that of the remote that answered the previous poll.
This is a 4-digit value, including the leading minus sign, expressed in dBm with a typical
accuracy of +/- 2dB. For example, a value of -090 indicates a signal strength of -90 dBm.
2.5.2.5 Local RSSI
Displays the strength of the last valid data signal received by the connected Integra-H unit.
The format described in the Remote RSSI section above applies.
2.5.2.6 Interpreting RSSI Readings
Typical values of RSSI will be in the range of -110 to -60 dBm (depending on network
speed), with higher values (i.e. less negative values) indicating a stronger signal.
Reliability of data reception depends largely on signal strength. Good design practice calls
for a minimum 30 dB “fade margin”, based on a threshold reception level of -107 dBm (1
uV) at speed of 9600 b/s. Experience indicates that this will give about 99.5% reliability.
Some representative performance values for 9600 b/s operation are given below. These
values assume that the units are correctly aligned and installed in a quiet location.
Environments with high electrical or RF noise levels will require an increase in the numbers
shown to achieve a given level of reliability.
-100 dBm
Approximately 50% reliability. Fading may cause frequent data loss.
-90 dBm
Approximately 90% reliability. Fading will cause occasional data loss.
-80 dBm
Approximately 99% reliability. Reasonable tolerance to most fading.
-70 dBm
Approximately 99.9% reliability with high tolerance to fading.
If RSSI values drops seasonally the most likely cause is tree foliage which can interfere with
radio transmissions during the spring and summer.
