Field instruments have a strict power budget
A growing share of instruments run away from the mains — in the field, in vehicles, on pipelines and in remote monitoring stations — and on battery power every component is judged on what it draws between charges. A switch in such a device has to do its job with minimal coil energy and without giving up the isolation or contact stability the measurement needs.
Sealed contacts for field conditions
Battery instruments do not usually enjoy a controlled lab environment. A reed contact is sealed inside its glass capsule, which keeps dust, humidity and corrosive atmosphere off the contact surface. The part therefore keeps working in locations where an open relay contact would oxidize or an exposed semiconductor connector would degrade.
Insulation where the measurement needs it
Two isolation barriers matter in a multi-channel meter: contact-to-coil, which keeps the control side separated from the load, and contact-to-contact, which matters when several inputs are scanned through one device. A closed reed contact adds low, stable resistance, so the same part is well isolated when open and low-loss when closed — the combination that preserves reading accuracy in a battery meter.
Coil power in the milliwatts
Reed relay coils are driven at milliwatt level, and the relevant series are offered across a broad choice of high coil resistances so the coil can be matched directly to a low supply voltage and the drive strength of battery-fed logic. Even a continuously energized channel then draws only a few milliwatts.
Magnetic latching: pay for the switch only at the moment of switching
For the tightest energy budget a magnetic latching (bistable) relay removes the holding current altogether. A roughly 2 ms pulse closes the contacts, a 2 ms pulse of opposite polarity opens them, and a permanent magnet holds the state between pulses with zero coil current. For an instrument that switches a channel on a schedule and then sleeps for minutes, the switching cost becomes a few-millisecond event rather than a continuous drain.
Where the combination is used
Portable data loggers and handheld meters use the relays to select ranges and route sensor inputs without drawing current between readings. Remote environmental and pipeline monitors use latching versions to switch channels or calibration paths only at scheduled intervals. Portable insulation and earth-resistance testers value a contact that switches cleanly on very little control power. The common design aim is to maximize time between battery changes without weakening the switching function — which is why the choice usually comes down to high coil resistance for always-on channels and magnetic latching for intermittently switched ones.
About SHR AUTOSENSOR
SHR AUTOSENSOR TECH LIMITED (SHR AUTOSENSOR) manufactures high-voltage reed relays, mercury wetted relays and high-voltage DC contactors. Contact: [email protected] | +86 13761571029 | www.reed-relay.com