All SDI-12 sensors use "M!"

Standard measurement command M! causes datalogger to wait for a response. For 1-2 sensors it's negligible but using 8 can result in skipped slow scans.

Might need to use concurrent measurements instead..

Sensor	SDI-12 command time	Time for heat storage msmts	Time for profiling msmts
CS650	600 ms	up to 1.2 sec	n/a
CS655	600 ms	up to 1.2 sec	n/a
5TM	1 sec	up to 2 sec	up to 6 sec
TDR series	1 sec	up to 2 sec	up to 6 sec

5TM sensors require 1 second for measurement:

Select SDI12 Port: 3
Entering SDI12 Terminal
?!
A
AM!
A0012
A
AD0!
A+1.00+20.6

Likewise, TDR series probes also require 1 second for measurement (see Table Command Reference in the user manual. Also worth noting:

If a cable is used to connect multiple sensors to the data recorder and if concurrent readings are to be taken the voltage drop in long cables may become an issue. For example: 5 sensors operating simultaneously could draw up to 400 mA of current and cause a voltage drop of 3.25 volts in 250 feet of 22-gauge wire. If the voltage at the sensor drops to the lower operating limit, the sensor may misread or fail to report data. To avoid this do not use concurrent commands or ensure that long cables are of sufficient wire gauge to handle the current loads without significant voltage drops. The SDI-12 command “aV!” can be used to measure the sensor supply voltage at the sensor and help diagnose power issues. However, the “aV!” command is not concurrent, and so it cannot measure the loading effects of concurrent measurements.)

wsular / EasyFlux-DL-CR3000

All SDI-12 sensors use "M!" #10