Can it measure silane, diborane and germane? How do I choose?
Yes. These three semiconductor hydride specialty gases are available on the TB420 in both ES1 and ES4 cell versions: silane 0 – 10 ppm (0.001 ppm resolution), diborane 0 – 1 ppm (0.001 ppm) and germane 0 – 5 ppm (0.01 ppm), all with a two-wire 4–20 mA output. A practical selection order is to treat the gas as flammable first and then confirm leakage at ppm level: silane has an autoignition temperature of about 21 °C and is pyrophoric (NFPA 704 flammability 4), with a flammable range of 1.37% – 96% vol and a relative density of about 1.12, so leaks are slightly heavier than air and accumulate low, in trenches and valve boxes — mount detection points near the leak source and low, not only overhead. The official cross-sensitivity table also shows 100 ppm hydrogen reading about 20 ppm on the silane channel (roughly 20% positive interference) and 1 ppm chlorine reading negative (about −0.5 ppm); where hydrogen or chlorine is present, subtract at system level or use separate channels.
How do I choose between 4–20 mA and a digital interface?
It depends on where the data ends up. Choose 4–20 mA when the value feeds an analog input on a PLC or DCS, when cable runs span tens to hundreds of metres, or when VFDs and heavy equipment are nearby — a current loop is insensitive to cable resistance and anything below 4 mA is inherently an open-circuit alarm. Choose a UART / I²C digital module (the TB200B and TB600B&C series here) for custom instruments that need temperature and humidity alongside the reading, custom algorithms, or battery power. Running both is common: distant field points over 4–20 mA, in-device points over a digital interface.
How is the two-wire connection made, and what supply is needed?
Two-wire means supply and signal share the same conductor pair with the module in the loop: the positive side takes 9 – 24 V DC (24 V recommended) and the loop current varies between 3 and 22 mA with concentration. On a PLC analog input, scale 4 mA to the bottom of the range and 20 mA to the top; a reading below 4 mA indicates an open circuit or fault, and a dedicated fault output pin can drive an alarm circuit. Total consumption is under 0.6 W. A higher supply voltage allows longer cable runs and more loop headroom.
Can it be used for %LEL combustible-gas alarms?
It does not replace a %LEL alarm, and this point matters. The TB420 is a ppm-level toxic and harmful gas module whose ranges and resolution are designed around occupational exposure limits and leak detection. The carbon monoxide 0 – 2% vol and oxygen 0 – 25% vol spans in the catalogue are extensions for high-concentration duty and oxygen deficiency or enrichment monitoring, not combustible-gas lower-explosive-limit alarms. For %LEL alarms, choose a catalytic bead or infrared combustible-gas sensor.
What are the accuracy, lifetime and warranty?
Accuracy is ±5% of the measured value with repeatability better than 2% and a linear output; expected lifetime exceeds 5 years, and a sensor lifetime self-test helps schedule replacement ahead of time. Warranty is 12 months from the date of shipment. Exact figures are stated in the official datasheet for each model, downloadable from its product page.
How do I get a quote, samples and datasheets?
Every datasheet is downloadable from its product page on this site. For samples and volume pricing, send us the target gas, range, cell option (ES1/ES4/EC4), the number of measuring points and annual volume through the contact form or by email, and we will quote the matching model and order number with lead time.
