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PDM Portable Dew Point Monitor
| PRODUCT | RANGE | OUTPUTS | RATING |
|---|---|---|---|
| Portable Dew Point Monitor | -148 to +68°F pressure dew point | 4-20 mA, two alarm relays | 145 psig sample; 23 to 122°F ambient |
Specifications
Configuration & Size
Model:
PDM, one model; other ranges and pressures by quotation
Sample:
2.1 to 10.5 scfh through 6 mm quick-connect fittings
Enclosure:
NEMA 4X polycarbonate, 11.2 x 5.3 x 8.5 in, wall or bench
Supply:
85 to 265 VAC, 50/60 Hz, 6.5 ft cord
Features
- A refrigerated dryer at full load should read 35 to 40°F; 50°F and climbing means an overloaded exchanger, a hot inlet or a failed drain
- Desiccant dryers read -40°F for ISO 8573-1 class 2 and -100°F for class 1, well inside the -148°F floor of the probe
- Built-in 0.3 micron sample filter and flow meter protect the probe and set the 2 to 10 scfh sample rate
- PTFE sample tubing and a protective carrying case are in the box
One instrument for every dryer in the plant
Refrigerated, desiccant and high-pressure dryers read on the same probe
The PDM is a self-contained instrument that puts a number on what a dryer is doing. A ceramic hygrometer probe reads pressure dew point from -148 to +68°F, or 0 to 3,000 ppmv, on a four-digit LED, with a 4-20 mA output and two alarm relays for a dryer alarm or a PLC. The sample line runs through a built-in 0.3 micron filter and a flow meter on 6 mm quick-connect fittings, so it can be carried from dryer to dryer for an audit or screwed to the wall as a permanent monitor. One probe covers the 35 to 40°F of a refrigerated dryer and the -40 and -100°F of desiccant dryers.
Permanent monitor when it stops moving. Two programmable relays: one for a dew point warning on the dryer, one to a PLC or the compressor controller; 4-20 mA output carries the dew point to a building system or a data logger for the ISO 8573-1 record; NEMA 4X case shrugs off a wash-down aisle or a compressor room; 85 to 265 VAC supply runs on any circuit; Accuracy of plus or minus 3.6°F is enough to see a dryer drifting from 38°F toward 45°F weeks before water shows up.
Prove the dew point, not the gauge. Sample from the dryer outlet after the afterfilter, from the top of the pipe, never from a low point where liquid collects; Give it 10 to 15 minutes to purge for a refrigerated reading and longer for a desiccant dryer while the tubing dries down; Read at line pressure below 145 psig; a sample regulated from 175 to 100 psig reads about 13°F lower than the true pressure dew point.
PDM Dew Point Monitor Part Numbers
| Part Number | Range | Connection | Rating |
|---|---|---|---|
| PDM | Single model; Options for other ranges and higher pressure by quotation | 6 mm OD quick-connect tube fittings | 145 psig |
The PDM is supplied as a single model with its sample filter, flow meter, tubing, fittings and case; other dew point ranges and higher sample pressures are quoted on request.
PDM Dew Point Monitor Applications
Dimensions and mounting
An 11.2 x 5.3 x 8.5 in case with the sample fittings and the cord on one side; bench, case or wall.
For an audit the PDM sits on the case lid or a bench next to the dryer, with the 6 mm PTFE sample tube run from a tapping on the dryer outlet pipe to the inlet fitting and the sample discharged to the room through the flow meter. Tap the pipe on top so the sample is air, not the condensate running along the bottom, and keep the tube short; every foot of tubing is another minute of purge before the reading settles. The sample cell is rated 145 psig, so on a 150 or 175 psig line the tap goes through a regulator, and the reading is then a dew point at the regulated pressure, not at line pressure.
As a permanent monitor the case mounts to the wall on its back through the enclosure feet, at eye height beside the dryer, with the sample tube coming up from the outlet pipe and the relay and 4-20 mA wiring leaving through the gland to the dryer alarm or the PLC. Leave room to open the lid and to reach the flow meter, and keep the case between 23 and 122°F; on an outdoor dryer skid that means a heated enclosure.
Confirm the sample pressure, the range and the wiring you need with the quote; the drawing above is representative of the standard case.
Common FAQs
4-20 mA, two alarm relays
- Model: PDM, one model; other ranges and pressures by quotation
- Sample: 2.1 to 10.5 scfh through 6 mm quick-connect fittings
- Enclosure: NEMA 4X polycarbonate, 11.2 x 5.3 x 8.5 in, wall or bench
- Supply: 85 to 265 VAC, 50/60 Hz, 6.5 ft cord
- Range: -148 to +68°F dew point, or 0 to 3,000 ppmv
- Accuracy: Plus or minus 3.6°F
- Sample pressure: 145 psig maximum
- Outputs: 4-20 mA into 500 ohm; two volt-free relays, 3 A at 240 V
- Ambient: 23 to 122°F operating, -40 to 167°F storage
