4 Digital LED Tachometer, Digital RPM Tachometer Speed Meter + Hall Proximity Switch Sensor for Measuring Temperature & Pressure, Red/ Blue(Blue)

Specifications: Measurement accuracy: ±0.1% Display mode: 0.56″LED Display refresh rate: >3 times/sec Working power supply: DC8-24V, 30mA, measurement range: 10-9999RPM  Hall proximity switch : magnetic Appearance size: 80 x 42 x 25mm/3.14 x 1.65 x 0.98inch LED display(Optional): red, blue Weight: 80g(red),105g(blue) Overrange display: the first one shows “1” or “-1″, and the latter three do not showPrecautions: 1. Connect the plug correctly according to the wiring diagram 2. Should avoid strong electromagnetic interference and it is better to use shielded wire or double stranded wire for measuring conductors 3. The counting signal of the counter and the switch of the zero clearing signal input or the circuit shall be as close as possible to the terminal of the counter to make the signal line as short as possible  4. Avoid with other such as: high voltage wires or power wires and so on with same tube or twisted  trace line, in order to avoid unnecessary interference necessary, please use the shielded wire, shielding layer connect the”+” of the count terminals 5. It is not recommended to use a mechanical switch or micro switch because they have a relatively short life span and can be counted by mistake after long time. If you use a mechanical switch or a micro switch, please try to use a better quality, so as not to miscount, and strongly suggest a magnetic control switchPackage Included: 1 x Tachometer  1 x Hall NPN proximity sensor