Hot Probe

Detector Tubes Need Gas at Normal Temperatures

This is the problem the hot probe exists to solve, and it catches people out because it’s rarely stated up front.

Gastec detector tubes are designed to measure gas at normal ambient temperatures. Each tube’s instruction sheet sets out its operating temperature range, which covers ambient measurement comfortably, and that’s what most tube work involves.

It doesn’t cover hot gas. Vehicle exhaust runs at several hundred degrees, and an incinerator flue, kiln, furnace or boiler stack can be hotter still. Drawing gas at that temperature straight into a tube means the reagent is working far outside the conditions it’s calibrated for, so the reading can’t be relied on.

Without cooling, hot gas can’t be measured with a tube, and the alternative is taking a sample away for laboratory analysis.

What the Hot Probe Does

The name is slightly misleading, because the hot probe is a cooling device.

It’s a cooling fin accessory that fits between the hot gas source and the tube. Gas is drawn through the probe by the sampling pump, and the probe cools it from as much as 600°C down to normal temperature before it reaches the detector tube. Gastec gives its working range as 60 to 600°C.

The tube then measures a sample at a temperature it’s designed for, and the reading is taken directly off the printed scale in the normal way. Cooling changes the temperature of the sample, not its composition.

That one accessory extends the whole Gastec tube range from ambient measurement into hot gas measurement, a considerable widening of what the system can do for a small addition to the kit.

The Holder Is Worth Having

The hot probe holder, No. 345A, secures the hot probe and improves its stability during sampling. Holding a probe in a hot exhaust stream while watching a tube and operating a pump is otherwise a three handed job.

There are two restrictions on the holder. It can’t be used with twin tubes, and it can’t be used with the oxygen tube No. 31B. Both are worth knowing before ordering, and neither stops the probe itself being used.

Where Hot Gas Measurement Comes Up

It’s wider than most people expect, once the capability is there.

Vehicle and mobile plant exhaust, which on a mine site or in a workshop means measuring what an engine is actually producing, rather than what the ambient air holds. Incinerators and waste to energy plant. Boiler and furnace flues. Kilns in cement, ceramics and glass. Crematoria. Flares. Process vents and hot ducts.

In several of those, the alternative is a full emissions analyser, which is the right instrument where continuous or multi parameter measurement is needed. Where the need is a single spot check on one substance, a tube with a hot probe answers it for a fraction of the cost, with nothing to calibrate.

What It Doesn’t Replace

It’s worth being clear, because the two are complementary rather than competing.

An emissions analyser measures several gases continuously, calculates combustion efficiency and mass emissions, logs data and produces a report. For combustion tuning, compliance reporting or any programme of measurement, that’s the instrument.

A hot probe and a tube give one substance, once, at one point. That suits a spot check, a verification, an unusual substance no analyser covers, or a site that needs the measurement occasionally rather than routinely.

Where It’s Used

Vehicle and mobile plant exhaust measurement. Mining and heavy vehicle workshops. Incinerators and waste to energy facilities. Boiler and furnace flues. Cement, ceramic and glass kilns. Crematoria. Flare and vent monitoring. Process ducts carrying hot gas. Any situation where a single hot gas measurement is needed and a full analyser isn’t warranted.