VT Operation

For more details see the Bruker VT manual.

Changing temperature and heater power

To change and control temperature functions, use the edte command.

You can change the temperature or maximum heater power using the Change or Set Max buttons on the front panel of the edte window.

Be careful about setting the heater power. On the 600 and 500, it is very rare that a maximum heater power greater than 5% is required as there is a discrepancy between this number and the actual output power. Do not use a number greater than 5% on the 600 and 500 unless you are sure you need it!! For temperatures around 298k a gas flow 500 litres/hour (top of ball on “5” on VT unit) is recommended for 5mm probes. For low temperatures, increase gas flow to ~700 litres/hour or more. If you increase the flow rate too much, the sample will partially eject itself (you will lose the lock etc.) Temperatures below ~273K will usually require liquid N2 operation – see Facility staff.

Note: Do not use samples in water or D2O below 278K as the water may freeze and crack the sample tube inside the probe. This is not good.

If the VT is operating well, the temperature will remain constant if your operating temperature is close to room temperature (283-313K).

Outside this range, often +/- 0.1K may be the best you can do, worse if you are near the extremes of the probe’s operational temperature.

If the temperature is oscillating wildly, the approach is either:

1. load a VT configuration file (quick)
2. do a self tune (up to 15mins, but the best result)
3. do both, a then b. Both of these affect the PID parameters, which control how the system responds to temperature fluctuations and affect how stable your temperature is.

How to load a configuration file

In the edte window select File->Load configuration->filename.

e.g., default conditions on the 600, load the configuration file: 298K_tbiz_500lh.tcf

(= temperature_probe_gasflow), this is designed for use at 298K with the (default) TBI-Z probe using a gas flow 500 litres/hour (top of ball on “5”). Look for the filename with the temperature closest to what you require and then set the exact temperature you want after loading the configuration file. If there is no configuration file close to the temperature you want and the temperature is unstable, you are forced to do a self tune.

How to perform a self tune

Wait till your sample is as close to the correct temperature as it will stay before starting the self tune, i.e., wait till it is oscillating either side of the temperature you want, don’t do a self tune when it is 5K off the temperature you want

To tune the VT unit, run edte then select Control->self tune to open the self tune window. Set the Self-tune heater power to 10.0 for best results Click the self tune button to start.

During the self tune process the A-T light on the Eurotherm unit will flash. The self tune process usually takes~5 minutes to run and then may take 10 minutes to settle down on temperature again.

The TBI-Z probe on the 600 takes the longest amount of time to stabilize.

During the self tune process, 3 phases occur:

Phase 1

The VT unit keeps the heating constant from the moment you start the self tune – the temperature may go up or down.

Phase 2

The heater is switched off completely until the temperature drops 3-5K below the required temperature

Phase 3

The heater is set to the maximum defined by self tune heater power and the temperature will increase well past the desired temperature, e.g., 10-15K. After this, the temperature should settle down

Note: Because the temperature oscillates during this process, be conscious of the melting and boiling points of your solvent, as either freezing or boiling samples can be catastrophic!

You can save your own temperature parameter files after doing a self tune – note temperature, probe, gas flow used.

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