Instructions

UM-0085-B09 DT80 Range User Manual Page 342
RG
 Frequency Measurement
The R channel option can be used to measure the frequency of an input signal, e.g.
RA1S 1HSC(R,RS)
will return the frequency in Hz of an input signal on channel 1C, while
RA10S 1HSC(R,RS)
will do the same thing but resolve down to 0.1Hz.
The
RS option divides the channel value (number of pulses) by the time since the last sample, yielding a frequency.
This technique can also be used for the digital input channels (1D-8D), e.g.
RA1S 7C(R,RS)
will return the frequency in Hz of an input signal on channel 7D, in the range 1-30Hz.
SDI-12 Channel
Not available on DT82I
About SDI-12
SDI-12 is a serial communications protocol for interfacing multiple microprocessor based sensors to a data logger. SDI-
12 uses a shared three-wire "bus" – 12V power, data (0-5V signaling levels) and ground – and operates at a data rate of
1200 baud.
Each sensor connected to an SDI-12 bus is configured with a unique address, which is a single numeric or alphabetic
character. The data logger specifies this address when it requests data from the sensor. This transmission will be
received by all sensors, but only the one with the matching address will respond. If two sensors have the same address
then they will both try to transmit at once, resulting in garbled communications.
The SDI-12 standard has undergone a number of revisions; at the time of writing the current version is 1.3. (1.0 was
released in 1988, 1.2 in 1996 and 1.3 in 2000.) Not all sensors support the latest version. The DT80 can determine which
version of the standard a given sensor supports, and act appropriately. Each SDI-12 message sent by the data logger is
a short (up to 5 characters) plain ASCII string, terminated by a ! character. The response from the addressed sensor is
also in ASCII format (up to 80 characters).
For more details see http://www.sdi-12.org.
SD1 – SDI-12 Sensor Inputs
The DT80's tri-stateable digital I/O channels (5D-8D on DT80, 4D on DT81/ 82E) can be used to control up to four SDI-
12 buses. Up to ten SDI-12 sensors can be connected to each bus.
As shown below, an SDI-12 bus is connected to the DT80 as follows:
• The SDI-12 DATA line connects to one of the digital I/O terminals 5D-8D (4D for DT81/ 82E)
• The SDI-12 GROUND line connects to the DGND terminal
• The SDI-12 POWER line may be connected to the DT80's external power input terminal (+), or one of the power
outputs on the DT85/DT80 Series 2-4 (12V or PWR OUT), or a separate 9.6-16V DC supply.
When connecting a sensor to the DT80 for the first time, it's best to connect only that sensor, i.e. you should temporarily
disconnect any other sensors on the same SDI-12 bus. This ensures there will be no address conflicts
Figure 165: Wiring for an SDI-12 sensor. Up to 10 sensors can be connected in parallel to each digital channel
To measure
Use the command
register #1 on SDI-12 device #0
7SDI12