Metal film resistors suitable for harsh environments

12th April 2017
Alice Matthews

A range of precision metal film MELF resistors with AEC-Q200 qualification has been launched by TT Electronics. Providing a combination of high precision and tolerance to surge conditions, the WRM-HP resistors are suitable for measuring supply line voltage levels in energy metering and power condition monitoring. The resistors complement TT Electronics’ existing WRM series, adding high power versions of the larger two sizes.

Their AEC-Q200 qualification makes them a suitable choice for reliable performance in harsh environment applications such as those found in automotive products. Aimed at industrial, instrumentation and automotive applications, the resistors will find favour with designers of energy meters, measurement instruments, process monitors and automotive control systems.

The WRM0204HP and WRM0207HP are rated at 0.4 and 1W respectively. The former specifies a maximum 5s overload voltage of 400 and the latter, 700V. Standard values from R10 to 1M0 are available in E24 and E96 ranges, giving plenty of scope for ‘close value match’ choice to designers. An ambient temperature range of -55 to 155°C is accommodated.

The resistors’ surge tolerance characteristics enhance reliability and reduce field failures. With precision levels of ±0.1% resistance tolerance and ±15ppm/°C TCR they free up designers’ error budgets, enabling savings elsewhere in the circuit.

Physically the resistors comprise a homogeneous sputtered metal alloy film on a high-grade ceramic rod. The resistance is adjusted to final value by a helical laser cut in the film, and the resistor body is protected by a lacquer coating. The resistors’ end caps’ pure tin finish comprise ageing free contacts onto which low melting-point solders can be used. WRM0204HP resistors measure 3.7x1.55, and the WRM0207HP, 6.1x2.4mm.

The company claims that, compared to key competing products, TT Electronics’ WRM-HP series offers the highest available rated power for a given load life stability and a higher 1.2/50ms lightning strike surge maximum voltage.

Driving the demand for this type of product is the growth in smart meters for billing and for site or process energy management, and also the demand for higher reliability automotive grade components. TT Electronics’ WRM-HP range of precision metal film resistors provides a combination of precision, high power rating and tolerance to surges.

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