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SDM-INT8 8-Channel Interval Timer
Services Available
Repair No
Calibration No
Free Support No


The SDM-INT8 outputs timing data to a Campbell Scientific data logger. The data logger can process the timing data to calculate RPM, duty cycle, velocity, crank angle, etc.

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Benefits and Features

  • Allows individual programming for each of the eight channels
  • Includes an internal microprocessor that allows measurement independent of data logger's execution interval
  • Outputs period, pulse width, frequency, counts, or time intervals
  • Records results as execution interval averages, continuous averages, specified interval averages, or capture all events


Detailed Description

The SDM-INT8 has eight channels that are individually programmed to record the timing of input voltage transitions (events). It uses this information to output:

  • Period (ms)
  • Frequency (kHz)
  • Elapsed time between events on adjacent channels
  • Number of counts measured on channel 2 between a “start” event on channel 1 and a “stop” event on any other channel
  • Elapsed time between events on channel 1 and any other channel
  • Pulse Counting (any channel can function as a pulse counter)

High Level Voltage Input Pulses Schematic

Low Level AC Voltage Input Schematic

SDM Operation

The data logger enables individual modules through an addressing scheme; up to 15 SDM-INT8s can be connected to one data logger. After a module is enabled, it operates independently of the data logger until additional commands are received or results are transmitted.


Operating Voltage 9.6 to 16 Vdc
Current Drain
  • 13 to 20 mA (active)
  • 400 µA (quiescent)
Maximum Timing Measurement 16.7 s
Resolution ±1 µs
Operating Temperature -25° to +50°C
Dimensions 0.3 x 12.7 x 2.5 cm (8 x 5 x 1 in.)
Weight 0.82 kg (1.8 lb)

High-Level Voltage Input Pulses

Minimum Pulse Width 2 µs
Maximum Frequency (32-bit values)
  • The maximum frequency specification for high-resolution (32-bit) values assumes all eight channels are used.
  • 5.1 kHz (averaging options)
  • 10 kHz (capturing all events)
Maximum Frequency (16-bit values)
  • The maximum frequency specifications for low-resolution (16-bit) values is for the execution interval averaging only.
  • If number of channels programmed is
    • 1 channel—42.5 kHz
    • 2 channels—17.5 kHz
    • 3 channels—11 kHz
    • 4 channels—8.6 kHz
    • 5 channels—5.2 kHz
    • 6 channels—4.8 kHz
    • 7 channels—4.5 kHz
    • 8 channels—4.28 kHz

Low-Level AC Voltage Input

AC Voltage
  • 20 mV RMS (min.) ac voltage
  • 20000 mV RMS (max.) ac voltage
Input Hysteresis 11 mV
Minimum Frequency 1 Hz
Maximum Frequency
  • 100 kHz (20 mV min. RMS)
  • 400 kHz (50 mV min. RMS)
  • 1000 kHz (150 mV min. RMS)
  • 4000 kHz (2.5 to 20 V min. RMS)


Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Data Loggers

Product Compatible Note
21X (retired)
CR10 (retired)
CR1000 (retired)
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR23X (retired)
CR295X (retired)
CR3000 (retired) SDMs are connected to the ports labeled SDM-C1, SDM-C2, and SDM-C3.
CR500 (retired)
CR5000 (retired) SDMs are connected to the ports labeled SDM-C1, SDM-C2, and SDM-C3.
CR510 (retired)
CR800 (retired)
CR850 (retired)
CR9000 (retired) SDMs connect to ports provided on the CR9080 PAM module.
CR9000X (retired) SDMs connect to ports provided on the CR9032 CPU module.

Mounting Equipment

Product Compatible Note

Distributed Data Acquisition

Product Compatible Note
Granite 10
Granite 6
Granite 9

Additional Compatibility Information

Data Logger Considerations


The SDMINT8 instruction controls the SDM-INT8 operation in CRBasic. Instruction 101 controls the SDM-INT8 operation in Edlog.

Power Considerations

The SDM-INT8 draws 20 mA. In most applications, the data logger’s sealed rechargeable power supply can be used. The data logger’s alkaline power supply has sufficient capacity to operate the SDM-INT8 during short-term installations only.

Enclosure Considerations

The SDM-INT8 should be housed in an environmental enclosure. A bracket is shipped with the SDM-INT8 for mounting it to an enclosure backplate.

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