Application Note # T15

Effects of temperature extremes

The first thing to stress is that Protovale's pulse-induction technique is inherently unaffected by changes in temperature, particularly in the usually sensitive search coils.
However, extremes of temperature (very low or very high) can have a noticeable effect. These are described separately under the headings of the effects upon the electronics, the batteries, the indicator displays, the mechanical properties of plastic parts, and suggested precautions; and these sections are further subdivided into the various models.

Electronics

The semiconductors used in the electronics are all commercial grade parts (not consumer/domestic grade) and generally specified for an operating temperature range of 0C to 70C (32°F to 158°F); however, to allow for additional temperature rises inside the electronics housing, it is prudent to derate the expectations to an ambient temperature range of 0C to 45C (32°F to 113°F).
In the majority of applications, it is only the low temperature limit which is likely to be met with in practice: we can not guarantee the exact performance of any model in below-freezing temperatures; and some effects may start to become noticeable as the temperature drops below about 10C (50°F).

CoverMasters CM5, CM52 and CM9:

The only observable effects are a slight loss of accuracy when processing the very strong signals associated with very shallow covers, of less than 35mm when using the CM5/52 with a standard head, or less than 20mm when using the CM9: in these cases, cover may be over-estimated by 1 or 2mm.

Totalscans TS2, TS6 & TS8, Rebar Plus, Pacetrace, and all models of Imp:

Since none of these models attempt precision measurements, there are no noticeable temperature effects within the electronics.

Batteries

Since these are electrochemical devices, they are subject to the fact that all chemical reactions exhibit a temperature-dependant "reaction rate". In non-scientific terms, chemical reactions (usually) proceed rapidly at elevated temperatures, but more slowly at reduced temperatures.
This means that batteries tend not to deliver full power or capacity when cold (but do recover when allowed to warm up). It also means that the self-discharge of rechargeable cells is more rapid at elevated temperatures.

All models:

There may be a reduction in operating hours at low temperatures.

CoverMasters CM5, CM52 & CM9, and Totalscans TS2, TS6 & TS8:

There may be a loss of charge when stored at elevated temperatures.

Indicators/displays.

Moving-coil meters may have a small temperature dependency; but since this is unlikely to exceed a few percent, it does not significantly affect their accuracy.
Liquid crystal displays will lose contrast at low temperatures, and the characters will appear faded; also, the displayed characters may appear "sluggish" to change. At elevated temperatures, the background may darken, which also reduces contrast.

CoverMasters CM5, CM52 and CM9:

The LCDs will lose contrast at extreme temperatures, becoming faint at low temperatures, and too dark at elevated temperatures.

Totalscans TS2, TS6 & TS8, Rebar Plus, Pacetrace, and all models of Imp:

There are no effects of any significance.

Mechanical/plastics

The electronics housings, and the handles or shafts of ground-searching instruments, are made of thermoplastic material (usually high-impact ABS) which implies a variation in mechanical properties with temperature: at low temperatures, they lose their resilience and become brittle (and the same applies to the PVC jackets of connecting cables); at high temperatures, they lose their rigidity as they become softer. The search heads are made of - or encapsulated in - epoxy resin, which exhibits less loss of resilience at low temperatures, and does not soften at high temperatures.

CoverMaster CM5/52, Rebar Plus, and Imp Wall-tie and rebar locators:

The leather case for the electronics, and the epoxy search head, mean that no significant problems arise.

CoverMaster CM9:

Again, no significant problems are expected.

Totalscans TS2, TS6 & TS8:

The Leather case protects the electronics; but the shaft of the search coil may lose strength at both extremes of temperature.

Imp 'C' and Imp Box Locator:

No problems have been experienced with the electronics housing; but the shaft of the search coil may lose strength at both extremes of temperature.

Pacetrace:

The electronics housing and shaft are both metal, and the search head is epoxy, so no problems are expected.

Precautions

Any instrument left overnight during winter in an unheated warehouse or outbuilding, or in the boot of a car, can become very cold; conversely, an instrument left on the rear parcel shelf of a sealed car during summer can become very hot. These represent "storage" conditions, and as such will not cause any permanent malfunction; but the instrument should be allowed to reach a more "normal" temperature before actual use.
Note also that low temperatures may be accompanied by condensation of water vapour (depending on the humidity of the air): whilst this should not cause any long-term damage, the instruments must be allowed to "dry out" at the earliest opportunity, and certainly before use.

All instruments:

If they have been exposed to low temperatures overnight or during storage, they must be allowed to "thaw out" before use: This can be done by keeping them in a warm room, but not by the direct application of heat.

CoverMasters CM5, CM52 and CM9:

In addition to allowing cold instruments to warm up, it is advisable to switch them on for half an hour or an hour immediately before use (on the way to the site, for example), as their internal dissipation may help to keep them warm; and similar considerations apply to the Totalscans.

Totalscans TS2, TS6 and TS8, and Imps with long-handled search coils:

Slightly more care than usual should be exercised in handling at very high or low temperatures, as the shafts of the search coils will not have their full accustomed strength.

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