Measurement and message intervals

The message interval is the time, in seconds, between the automatic message transmissions. It can be set between 2 to 600 s (0 gives polled messages). The default is 10, meaning a message will be sent automatically every 10 seconds. The message interval must be a multiple of the measurement period.

The backscatter average time, BS_Av_Time, is the period over which the laser is firing and taking measurements.

The measurement period is the time interval between the start of backscatter average time (BS_Av_Time), during which the laser fires, and the start of the next measurement period. The measurement period must be long enough to include the backscatter average time and some processing time. The minimum measurement period is 2 seconds, which assumes the backscatter average time is 1 second. The measurement period can be set between 2 to 600 s (default is 10 s). If it is set to 0, then measurements must be polled.

The rolling average (1 to 29, default 1) is the number of periods used to calculate each scatter value that is either used in a profile message or in a calculation of cloud height.

The message interval chosen may affect measurement parameters allowed within the BS command, which can be used to set non-standard measurement parameters) as follows:

If message interval = measurement period = 2 (the lowest values allowed), then the backscatter average time (BS_Av_Time) must equal 1 and the rolling average must equal 1.

If the message interval is between 3 and 9 s, then the measurement period must be the same as the message interval.

 

In the following examples, yellow means laser firing.

To comply with the requirements for Sky Condition the total measurement period for rolling averages should not exceed 30 seconds.

In this case, the SkyVue PRO sends a message every 2 seconds based on one measurement averaged over 1 second. Therefore, each message is based on a single 1 second period of backscatter average data.

Laser firing (yellow)                                              
(BS_AV_Time) = 1 s 1 s                                            
Measurement Period = 2 s 2 s                                          
Message Interval = 2 s 2 s                                          

In this case, with the rolling average set to 1, the SkyVue PRO sends a message every 30 seconds. It takes three, 2 second, measurements at 10 second intervals. Only the last measurement is used in the output message but all three are used for calculating sky condition. Therefore, each message is based on a single 2 second period of backscatter average data.

Laser firing (yellow)                    
(BS_AV_Time) = 2 s 2 s                                      
Measurement Period = 10 s 10 s 10 s 10 s                
Message Interval = 30 s 30 s                

In this case, with the rolling average set to 3, the SkyVue PRO sends a message every 30 seconds that contains the average of the latest three measurements. Therefore, each message is based on three, 10 second measurement periods, with each containing 2 seconds of backscatter average data.

Laser firing (yellow)                                            
(BS_AV_Time) = 2 s 2 s                                          
Measurement Period = 10 s 10 s 10 s 10 s                    
Message Interval = 30 s 30 s                    

In this case, with the rolling average set to 3 (default), the SkyVue PRO sends a message every 10 seconds that contains the average of the latest three measurements. Therefore, each message is based on three, 10 second measurement periods, with each containing 2 seconds of backscatter average data.

Laser firing (yellow)                                            
(BS_AV_Time) = 2 s 2 s                                          
Measurement Period = 10 s 10 s 10 s 10 s                    
Message Interval = 10 s 10 s 10 s 10 s                    

In this case, the SkyVue PRO sends a message every 14 seconds based on one measurement taking 4 seconds over a 14 second interval. Therefore, each message is based on a single 4 second period of average data.

Laser firing (yellow)                                
(BS_AV_Time) = 4 s                                
Measurement Period = 14 s 14 s 14 s       14 s       14 s      
Message Interval = 14 s 14 s 14 s 14 s 14 s      

This message cannot be set up using the MCFG command alone.

The BS command has to be used as follows:

BS_Av_Time (averaging period) has to be set to 4, not the default value.