The small cup on the floor represents an application which needs to be cooled.

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For controlling a temperature, mode 8 is a control mode with 1 sensor.

In this mode only one sensor is mounted on the surface of the object which need to be cooled. The pump will start cooling until the wanted temperature is reached, and then starts slower pumping to maintain the temperature, resulting in a small stream of LN2, sufficient to keep this temperature.

The wanted temperature can be set by the potentiometer on the side of the pump, or send by an external 0-5 Volt analogue signal.

In this way any object could be cooled and be set on a fixed temperature. The accuracy of the result is highly dependent of the mechanical setup. For every application the placing of the sensor should be carefully determined, and the place of where the LN2  enters the application should be chosen. Thermal insulation of the application should be optimal designed.

If there is the need to have the temperature as steady as possible, you could use a small heating device to help keeping the wanted temperature. There is an output on the pump which can steer a power supply for a small heating device. The pump will steer the heater when the temperature of your application drops too far. Because the dosing of LN2 has a certain mechanical delay, and an electric heating is much faster, this heating can compensate the delays in cooling, resulting in a steady temperature of +/- 1 degree Celsius. But this is highly depending of the mechanical setup.

A common application is cooling a bath with a spiral coil, or any other way of separate reservoir, for keeping the LN2 separated from the to cool object.

In this way that coil (or other reservoir) will be filled with LN2, enough to create the cold to cool down the object to an requested temperature. In this way the temperature is measured in the bath, but the level in the coil should not come too high, so that it may overflow. When this setup starts cooling down, it may need a lot of cold, and only looking at the wanted end-temperature, may cause that LN2 is adjusted too much, so that the coil overflows.

For this purpose we have working mode C, which is almost the same as mode 8,  in which an extra level sensor makes the pumping STOP when this sensor is touched by LN2. By placing this sensor at the highest possible level in the coil, this will prevent the coil for overflowing.

In this example the coil or reservoir on the cold finger will be filled to keep the temperature from the temperature sensor steady, but the pump will STOP if the coil is too full, or the reservoir on the cold finger is too full.

Controlled freezing curves

Based on mode 8, it is possible to create a complete defined freezing pattern. For this you need a presetted temperature curve which should be steered to the pump. You may use the analogue 0-5 Volt signal to tell the pump which temperature to keep, but better you use a #915 pump and put it in mode E and use the supplied freezing program to create your curves, and monitor the behavior, and log your data.

With the #915 pump you have 15 working modes. All modes from the #905 and #910 pump, plus two modes for steering direct by PC, by RS232 line. (serial interface)

With the supplied freezing curve program, you may set a freezing curve like the example below. You may set 24 temperatures, and set the time between these temperature. The system will dose LN2 until the wanted temperature is reached and will try to keep the temperature as close as possible to the wanted curve. If an external heater is connected, the heater will help to prevent overshooting. If the right mechanical setup is created, it could be possible to follow the curve within 1 degree Celsius, like in this example.

In this example the blue line is the wanted temperature, and the red line is the measured temperature on the sample.

This example was a 30 liter aluminum container in which the environment temperature needed to be controlled. LN2 was dosed at the outside, and the sensor was inside, with a ventilator to mix the air. A heater wire was surround the container, so the temperature was controlled by cooling with LN2, and heated by current.

In this situation we choose to use cooling from the outside, but also you could inject the LN2 into an airstream, or spray it onto your object, or create a cool-finger to cool your object. We used in this example heater wire to warm the object, but for smaller objects we can use halogen lamps to warm it up.

You may understand that for controlling temperature the mechanical setup is very important.

Let us help you in selecting the most optimal solution for your cooling problems. Fill out the contact form in the left column, and we will contact you and  find a proper solution for you.