WiFi Sensors
Click on the Questions below to View the Response.
1) What's the Difference in Performance in the WiFi B' versus G Sensors?
Connect Time (using Aironet Router) B Product: up to 2 seconds G Product: < 150 msec.
Security B Product: none, WEP 128 and WPA2-PSK G Product: none, WEP 128, WPA-PSK TKIP, WPA2-PSK AES, and WPA/WPA2-PSK mixed mode
Range (open field) B Product: 600 feet (18mw radio) G Product: 900 feet (63 mw radio)
DHCP B Product: needs to obtain new IP address for each transmission G Product: has DHCP caching, holding the lease until the IP address is no longer valid
Auto Channel Scanning B Product: significant impact on battery life G Product: minimal impact of battery life
On-Board Logging B Products: not available G Products: logs measurements, events and alarms (2 min. to 1 hour log interval – 3072 record buffer)
Wireless Configurability B Products: not available G Products: wireless configuration of non-network parameters ready (e.g., alarm limits, xmit intervals, retries, log intervals, etc.)
The battery life is similar on both products.
2) Does the Tries value only apply to the initial Beacon transmission, or does it apply to all transmissions (i.e. responding to Config requests, Log requests, etc.)?
The sensor will try again if it has not received an acknowledgement command (0x06 or 0x09) or if it has not exhausted its tries.
3) How does the WiFi Sensor Clock work?
The sensor clock is a 32-bit “relative” clock. It is up to the host software to relate this time to a meaningful time (accounting for timezone offset and daylight savings if needed). In our software we provide the sensor logged data times in the sensors local time.
Below is a snippet from our Extended Point Sensor Spec.
Time Calculations The sensor clock is not synchronized to any source. It is set to zero at the factory and will run when turned on. The clock does not run when the sensor is turned off. The sensor does keep the clock value while turned off. The Sensor Clock is 4 bytes and is in seconds. Note: UTC time should be used in the time calculations. A time adjustment must computed by subtracting the Sensor Clock in the beacon packet from the host current time at the time when the beacon packet is received by the host. Time Adjustment = Host Current Time – Sensor Clock To compute the time stamp for a History Log record: Time Stampn = Time Adjustment + Time Header + History Log Time Offset1 * 30 [+ History Log Time Offset1 * 30 + History Log Time Offsetn * 30] Where n is the number record position (starting at 1) in the Block. Note: With regards to the History Log Time Offset, if an Alarm Log precedes the History Log, as far as calculating time is concerned, the Alarm Log record is skipped (ignored).
5) When I am configuring the sensor, which is now connected to the computer via USB cable, do I have to set Destination IP = IP of this computer in the WLAN that includes the AP?
The destination IP is set to the IP address of the Host computer you plan to send data to. There is no need to set to the local computer during configuration. Instead, you would simply put the destination IP (or hostname) of the host computer/server that the UDP data will be sent to.
6) After sensor configuration I would like to set Destination IP to the Server IP, a computer located anywhere on the Internet, running the web page instrument. How do I do that?
Our tag sends data to Server IP, UDP port 50007. The Server is running the web page instrument.
As indicated above, you would configure the sensor to have the destination IP of the host computer/server that you want it to send data to. You also can configure/change which port to use for the UDP data (the default port is 6767).
7) Will the Temperature/Humidity module send data to a Server IP, UDP port 50007 if this is what we set in the Destination field?
Yes, this is correct.
8) Messages from the module to the Server IP are UDP or TCP/IP?
The sensor sends UDP packets.
9) If I choose a 4 min. transmit interval does it means that the module has a sleep time of 4min, and every 4min will send a message to Server IP via AP, message containing module MAC, Temp, Humidity, sleep time?
While the sensor is never completely asleep, this is essentially correct. The transmit period indicated at what interval the sensor will transmit a beacon packet with current data. While the sensor transmits regularly at this interval, there are battery life advantages of setting the transmit period to a longer time period and using the alarm limits to make sure you don’t miss critical data. The sensor samples the input variable every 15 seconds (regardless of transmit period) and compares the value to the alarm/time limits programmed in and if the sensor variable is in alarm, it will transmit a data packet immediately.
10) Are the alarm values part of the transmission? So we can detect the alarm in the web page software?
The sensor will use the alarm limits to transmit data packets immediately, and to initiate both the buzzer and LED for local audible and visual indications of an alarm condition (sealed sensors only support visual indication of the alarm). The alarm information is included in byte 72 of the 75 byte UDP packet (see attached data sheet with packet specification).
11) What does Alarm On Exit do if checked?
By selecting the Alarm On Exit checkbox, you tell the sensor to transmit a packet when it determines it is no longer in alarm rather than wait for the next transmit period. This gives the host software the ability to determine/report how long the sensor was in an alarm condition.
The ping tool allows you to determine if the sensor and/or computer can reach other computers and/or the destination host computer on the network. This is useful in troubleshooting possible network conflicts.
12) Now that everything is OK with the module, should I go back and change Destination IP to the Server IP where the web page instrument is (will be) running?
Yes. As mentioned above, there is no need to set a temporary destination IP if you don’t plan to send data to that address.
13) What is the function of the Push button on the side of module?
After configuring, you disconnect the cable as the sensor does not transmit data while connected to the USB cable. Pressing the button on the side has a couple of functions:
1) – Sends a special “service” packet typically used to add sensors to software system (this is the recommended method for adding sensors to a system – you would design the software to look for these “service” packets to add to its database). The normal packet for the temp/humidity sensor has a device type of 52 (the sensor packet starts at byte 34 of the UDP packet) and the “service” packet has a device type of 51. This button also allows you to force the transmitter to send a packet rather than wait for the normal transmit period packet.
2) If the sensor is in alarm, you can silence the buzzer by pushing this button.
14) My expectation is that after the module is disconnected from the USB cable, and maybe the push button is pressed, the module starts transmitting data to Server IP every 4 min. Is that correct?
If the sensor is turned on and not connected to the USB cable, then it will start transmitting (even without pushing the button). As mentioned above, pushing the button forces the transmitter to transmit a “service” packet.
15) Is this UDP data at port 50007 (if configured this way)?
If YES, then we will need to write code to read UDP packets at port 50007 as web application backend.
16) What is the transmission power for the b/g transmitters? What is transmission power for the b-only transmitters?
The transmission power for the b/g transmitters is 63mwatt and the transmission power for the b transmitter is 16mwatt.
17) Have you seen much variance with APs in terms of their receiver sensitivity affecting transmission ranges, etc.? I would suspect that the radio receiver sensitivity of the APs would have a huge impact on the reliability & distances that can be achieved.
Since we typically don’t deal with the end users, we don’t have any experience with radio receiver sensitivity of AP’s beyond the Cisco AP’s we’ve tested in house. These AP’s are the high end AP’s that you would likely see in hospital/office installations. We have found that we have don’t get as much range when using your lower end home type AP’s.
18) In terms of a pre-planning site survey, or transmission debugging…is there something that can be used to determine whether there is solid send & receive signal levels - hardware devices, software tools, etc.?
We would recommend using the tools that are built into the configuration utility (i.e. contact destination host, connect time test, etc.).
19) What is the best orientation of the transmitter for optimal RF performance?
In an indoor environment, the orientation of the transmitter will not have any effect on the radio performance.
20) What we're seeing is that we'll receive the beacon packet sporadically (maybe 1/3 or 1/4). The software detects that it's missed some data based on the Next Log Rec setting in the beacon packet & requests log history. However, the transmitter almost never responds to the log data request.
We have seen in a few installations that if you configure the transmitter to not cache the DHCP settings, the data delivery is more reliable. To turn DHCP cache to off, you must edit the configuration utility’s.ini file and set DHCPcache=0.
21) What is the minimum recommended dBm level we should be looking for from the configuration utility status for good communication? I think that for some of the transmitters in question it was in the -50's.
We recommend -70 or better.
22) Are the dBm values an indication of a) the transmitter's transmit power or b) the received signal from the Access Point?
This is the received signal from the Access Point.
23) How long does the transmitter radio stay on listening for an acknowledgement after sending the beacon?
2 seconds.