Here is one way to do it. (I guess rextended will comment the on-error 
)
On RouterOS v7 temperatur and volt are stored differently, so this script get it from both version.
Look at my complete script for Splunk here:
http://forum.mikrotik.com/t/tool-using-splunk-to-analyse-mikrotik-logs-4-0-graphing-everything/153043/1
:do {
# New version
:foreach id in=[/system health find] do={
:local health "$[/system health get $id]"
:set ( "$health"->"script" ) "health"
:log info message="$health"
}
} on-error={
# Old version
:if (!([/system health get]~"(state=disabled|^\$)")) do={
:local health "$[/system health get]"
:set ( "$health"->"script" ) "health"
:log info message="$health"
}
}