filling example for small dewar, cryostat or InfraRed detector

For many applications there is a certain small reservoir for cooling your detector or an other form of cryostat or LN2 trap, which is needed to be filled with a minimum level of LN2.

Nitrogen filling in this way can be used for cryogenic freezing of many objects, and filling of any type of cryogenic dewars such as for a Xray detector, infrared detector, MCT detector, infrared camera, laser detector, GDA detector, CCD cryostat, cold trap, or as a spot cooling system or any other cryostat cooling.

Because of the small diameter of the fill hose, you can use this cryogenic pump as a liquid nitrogen injector for any nitrogen cooled detector or cryogenic vessel.

Because of the very low adjustable pressure and the absence of a liquid nitrogen valve, with our liquid nitrogen cryogenic pump system it is possible to create very small flows which minimizes your application disturbance, like you have an automatic LN2 tap.

For this purpose, the #905 pump is sufficient for setting up an automatic filling procedure.

The #905 system has 6 different working modes, selectable with a little switch inside the pumphousing. For keeping a little external reservoir filled, modes 3, 5 and 6 could be used. Each mode works in a different way. You may select one mode and set up your application, but if this does not fulfill your needs, you may change the working mode later to see if this is better for your application. See for the other working modes in the left column, or go to HOME page.

Simplest Filling mode

Most simple is working mode 3, which is automatic FILL control with timer (1 sensor).

Working mode 3 = automatic FILL control with timer (1 sensor)

In this mode only one temperature sensor is mounted at the high-level which you want the LN2. With the Monitor software (needed only once) the time-interval for the pump to restart filling can be programmed. Your application will be filled until the LN2 level reaches the sensor, and then shuts off. After the presetted time is elapsed, filling starts again, until the sensor again is reached by the LN2 level.

If you are sure that you application does not 'dry out' in a certain time, you could use this mode.

Example: If you have a small reservoir which has a stand-time of 8 hours, you could use this mode and let it refill every 6 hours. In this way you are sure that every 6 hours it will be refilled, and your application is always cold.

Advantage: You only need one sensor (3 mm diameter) and the standard fill hose of 6,25 mm, so you can use this mode for very small entry holes. Also in this way you know when you can expect a filling action, when in the case a 'sudden' automatic filling action could spoil your measurement.

More advanced filling mode

To be absolutely sure that the liquid nitrogen level in your application is between two certain levels, you could use mode 5, which is control with a high- and low- level sensor.

Working mode 5 = 2-point level control (2 sensors)

In this mode two sensors are mounted, one at the lowest level , and one at the high-level which you want the LN2. Your application will be filled until the level reaches the HIGH-sensor, and then shuts off, until the LOW level sensor dries out. Then filling starts again, and stops when the HIGH sensor is reached.

Example: If you have a small reservoir of 10 cm high, you could use this mode and mount the LOW sensor 3 cm from the bottom, and the HIGH sensor 3 cm from the top. In this way you are sure that the level is always between 3 cm and 7 cm, and that your application is always cold.

Advantage: If the stand time of your application depends on variable parameters, this is the safest way to make sure that your application is always cold.

Disadvantage: The next refill action could be somewhat unpredictable, and fall into the time of a critical measurement. But, this could be more predictable if you, before a critical measurement, restart the pump by hand, so that your measurement starts with a full filled application.

Most advanced filling mode

To be absolutely sure that the level in your application is at exactly the same level (within 1 mm) you could use mode 6, which is an analogue level-control with one sensor

Working mode 6 = 1-point level flow control (1 sensor)

In this mode only one sensor is mounted exactly at the level which you want the LN2. Your application will be filled until the level reaches the sensor, and then starts slower pumping to maintain the level there, resulting in a small stream of LN2, sufficient to keep the level. This could be useful if a level-change influences your measurement.

Example: If you have a small reservoir of 10 cm high, you could mount the sensor 5 cm from the bottom. In this way you are sure that the level is always at 5 cm and that cooling of your application is always consistent.

Advantage: If your measurement is dependent of the LN2 level, this is the optimal way to make sure that your level is consistent

Disadvantage: The pump and the fill-line is continuous cold, so the amount of LN2 needed to keep this all cold, will be more than in mode 3 or mode 5.

With the #905 pump setups like above can be achieved. If you want a control based on temperature, you may need a #910 pump, or if you want all driven by RS232, you may need a #915 pump.

In all working modes, mount the filling hose in a way that the fresh LN2 can not 'splash' and reach the level sensors. If a drop of LN2 splashes on the sensor, the sensor could make shut-off the pump too soon. If possible, mount the supplied (yellow) phase separator 2 cm above the highest level, and away from the sensors, so that the gas- and liquid stream does not disturb your level.

If the application is very small, mount the sensors in an extra teflon protection tube, with holes, so that splashing LN2 can not reach the sensor(s) directly, but in a way that a rising LN2 level also will rise inside the protecting tube.