Features: Digital meter adopts new A/D conversion chip and high stable benchmark IC. Use surface mount components, circuit design is reasonable. Can be applied to measure voltage, current, also can connect to external sensor to measure temperature, pressure, displacement and other parameters. Easy installation, appropriate for use as all kinds of digital instrument display. Good stability, high measurement precision, strong anti-jamming capability. Specifications: Input Pulse Signal: NPN open collector, contact switch, contactless switch, level pulse Input Signal Voltage: -30V-0.6V(low level); 4-30V(high level) Measure Frequency Range: 9999Hz, 999.9hz, 99.99khz (automatically switchable) Max. Input Frequency: 10KHz/100khz/300khz Measure Accuracy: ±0.1%±1digit Display: 0.56 green LED Display Refresh Rate: >3times/second Power Supply: DC8-24V, 30mA Size: 8*4.2*2.6cm/3.14*1.65*1in Mounting Size: 8*3.9cm/3.14*1.53in Over Range Display: The first digit displays "1" or "-1", other three digits no display Note: 1, Connect wires correctly according to the wiring diagram. 2, Strong electromagnetic interference should be avoided, measuring lead had better to be shielded cable or twisted-pair cable. 3, Counting signal and reset signal input switch or circuit should be near the counter terminals, making signal cables as short as possible. 4, Avoid wiring in same tube or twisted with high voltage electric wire or power wire, in order to avoid unnecessary interference. If necessary, please use shielded cable, shielding layer on the counter terminal "+". 5, Mechanical switch or microswitch is not recommended, because of their relatively short life may cause mistakes after long time use.If using mechanical switch or microswitch, please try to use ones of better quality, in order to avoid error count. It is strongly recommended to use magnetic control switch. Package Includes: 1 x RPM Meter 1 x Hall Switch Sensor 1 x Cable .