Digital temperature probe placement

[East Coast]

Placing my temp probe the recommended 6" from a 400w HPS in cooltube with a 550m3/ph centrifugal fan pulling @ 260v (variac overdrive on a 240v circuit NZ ) and passive air intake temp around 18 degres 'c' - I cannot get the temp to 26 degres 'c' at canopy height.

When I lower the canopy height to 12" - Perfect, the temperature controller switches between the fan, now on 80v (nice slow drawing speed), and very rearly switches to heater - from a set-point of 25.5c and a differential of 0.3c.

So, what is your method of temperature probe placement?

There is this chart - "Optimal Distance Range" circulating, the distance from bulb to best foot-candles, i.e 400w hps =6".........600w hps =8"..............1000w hps = 10" ....................I realize this is where the optimal distance starts from, and you basically have 15" of room to place with before the foot-candles drop right off......but has any achieved the above 'optimal distance' - if so, how?

Cheers

 

[no clue]

Optimal Probe Placement...seems personal

 

[East Coast]

Optimal Probe Placement...seems personal

In the trade, it is called a 'sigmoidoscopy'

 

[kinddiesel]

I place my temp probe directly into the soil and the other plant height . so I know both temps, very important to know soil temp if over watered they root will rot. if cool soil the chance of rot is far less.

 

[East Coast]

Not many people use digital temp probes?