I want to incubate my sample at 50ºC and then slowly cool it down to 4ºC at a rate of 0.1ºC/s. I am using AB Veriti thermal cycler. Does anyone know how to set up the rate of cooling? It has to do something with the ramp rate, which is given in % but I don't know how to convert this into a real rate.
If I recall correctly (from when I interned at ABI), you can't directly set this in the Veriti interface. However, (again, I'm not 100% certain -- I couldn't find anything to confirm this after 30 minutes of googling,) the ramp rate percent refers to the percent of maximum ramp rate for the heating block.
According to the product website, the max heating block ramp rate is 5 °C/s while the max sample ramp rate is 4.25 °C/s, so you need a ramp rate between 2% and 2.4%.
As Thomas pointed out, there is a maximum ramp rate which you can set up on the thermocycler. Its value can go from 0% to 100%. I can then assume that a 100% ramp rate will corespond to the maximum ramp rate of 4.25°C/s for the heating block or 5°C/s for the sample. which means that a ramp rate of ~2.4%. Subsequently, I set up my reaction at a 2% ramp rate, as I started a timer at the time the ramp cycle started. To my surprise, the temperature was cooling down too slowly. Thus, I empirically found out that a ramp rate of 5% corresponds to ~0.1°C/s cooling speed.
I wished there was more precise way to calculate it. Perhaps the slope of the line changed at different temperature intervals. It would be great if I can talk to the AB people so that they could justify my finding.