You can buy a sensitive differential pressure guage that will do the same thing.
In those circumstances, pressures are measured in INCHES of WATER.
SO: if you want to go the DYI route you pick a location where you want to monitor the pressure and you bring tubes from INSIDE the enclosure and OUTSIDE the enclosure. You connect these tubes to a U shaped glass or plastic (transparent) section of tube with arms on the order of 10 to 18". Before connection you put some WATER in the tubes to fill each arm about 5". When you complete the connection the DIFFERENCE between the water level in each side of the "U" is the pressure inside your room.
You can buy "scientific" versions of the above thay feature a large (very) diameter tube on one side and a sloping tube on the other side. For pressure differences of a fraction of an inch, the sloping tube permits a more accurate measurement.
But, basically, all you need is some clear tubing, a ruler, and some water.
If all you want to do is be able to monitor the pressure difference: search "differential pressure gauge" at
. There's zillions of varieties and prices.
If you want to actually maintain (control) the pressure difference by varying the damper postion you could use a differential pressure transducer or transmitter as input to a PID controller. The output of the controller would then control a proportional damper actuator. Or you could keep the damper stationary and use the differential pressure transducer as input to a Variable Frequency Drive (VFD) to control the blower motor speed (assuming you have a three phase power system). Many standard VFDs have built in PID control functionality so you wouldn't need any other control devices but the transducer and the drive.
probably has whatever gauge, transducer, PID controller (no VFDs), etc. you would need.
You've received some good answers to your question, but no one has suggested that you will need to filter the incoming air. Although I hope you've already taken that into consideration, outside air only appears"clean". Check the outside air filters (if you have them) on your HVAC units for a good example of what is in the air you intend to put into this clean room, and that's only the big stuff! Depending on your process, material you can't readily see with the naked eye will contaminate the area.
Without specifying your application one can only guess as to the need for climate control (heat, and humidity, etc.), and the need to disconnect any normal HVAC units now serving the area (this will affect the pressure gradient measurements, and introduce contaminates).
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You monitor humidity if the process requires a certain range of humidity.
Your basic clean room is pressurized so that "leaks" take conditioned air out and un-conditioned air doesn't come in. The "conditioned" make up air would have to have moisture added or taken out as required by the process.
It sounds to me like the slack tube manometer may be the easiest solution with the magnehelic guage being the most elegant. One thing with slack tubes, the water evaporates pretty fast so you probably want a more stable operating fluid. You can calibrate your "ruler" to anything from mercury to motor oil.
True. Have made them using a 'pinch' in the ends to help this. And adding a small amount of oil on the water surface (be sure to add the same 'thickness' to both sides) will make the water last a long time. Have seen some using a red oil that also makes reading against the scale easier.