Monitoring Digital State
The dataTaker 50 has 5 digital input channels, and the dataTaker 500/600 series loggers have 4 digital input channels. The digital input channels can be used to monitor digital state.
The Channel Expansion Module (CEM-AD) has 20 digital input channels, which can also be used to monitor digital state.
Monitoring digital state can be implemented in 2 ways
digital bit states, where the digital state of a single digital signal is applied to a single digital input channel. The digital bit data is returned as 0 or 1 with units of State
digital byte state, where
The data reflects the bit pattern of the digital input channels.
Digital state signals may be from a variety of sources, such as contact closures, switches, optical sensors, logic circuits, etc.
The digital input channels are normally high or true when open circuit, because each is internally connected to the internal 5 Volt supply via a 10 KOhm pull up resistor.
Since the digital input channels of the dataTaker are bi-directional, the present output state of the channels can be determined by reading the channels as digital bit or byte inputs.
Connecting Digital Bit Inputs
The digital bit inputs are connected to the digital input channels between the selected digital input channel terminal and any GND or unused Analog Return terminal as follows
Figure 113 ñ Connecting Digital Bit Inputs
Note : If the Analog Return terminal is used as the return connection, be aware that this is 100 Ohm above the dataTaker ground.
Reading Digital Bit Inputs
Digital bit signals connected to the dataTaker are sampled and the data is returned when a Schedule containing the channel is executed.
Using DeTransfer, the command for example
R5M 1DS 4DS
instructs the dataTaker to measure the digital state of the signals applied to the digital input channels 1 and 4.
The DS specifies a digital bit signal applied to the digital input channel.
Using DeLogger, digital bit inputs connected to digital channels can be measured by the following Program Builder program. Digital inputs are selected directly from the channel selection walking menu.
Data is returned as 0 or 1 with units of State, depending on the state of the digital bit input.
The dataTaker will read the inputs every 5 minutes, and readings are stopped by entering a H (Halt) command.
Connecting Digital Byte Inputs
The individual bits of the digital byte inputs are connected to successive digital input channels between the digital input channel terminal and any GND or unused Analog Return terminal as follows
Figure 114 ñ Connecting Digital Byte Inputs
Digital byte measurement per se has limited value with dataTaker, because there is only a limited number of bits (channels). However the digital byte is useful if you need to read several digital bit states simultaneously. The result is a decimal value which will indicate the pattern of set and unset bits.
Reading Digital Byte Inputs
With digital byte inputs, where there are a number of digital channels involved, the channel number for the byte is the first channel of the byte. For example, if a 3 bit byte is connected to digital channels 2, 3 and 4, then the channel number for the byte is 2.
The dataTaker 500/600 series loggers can read up to a 4 bit byte, the dataTaker 50 can read up to a 5 bit byte, and the CEM-AD can read up to a full 8 bit byte.
The digital byte is assumed to include all digital channels from the starting channel nominated (as the byte channel number) to the last available channel or the eighth channel along, whichever applies. Therefore the default byte from say channel 2 will be a 3 bit byte for dataTaker 500/600 series loggers, a 4 bit byte for dataTaker 50, and an 8 bit byte for the CEM-AD.
If you do not need all subsequent channels from the first channel, then a mask can be set to indicate which channels are in the byte. The mask is a decimal value which is the binary pattern of the channels in the byte, and is entered as a channel option. For example a mask value of 6 (binary 0110) would mean that only channels 2 and 3 are in the byte.
The default mask value is 255, which means all channels up the next eighth.
The digital byte inputs are sampled and the resulting data is returned when a Schedule containing the channel is executed.
Using DeTransfer, the commands for example
The first command instructs the dataTaker to measure the digital byte of the signals applied to the digital input channels 1 through 4 inclusive (dataTaker 500/600 series) or input channels 1 through 5 inclusive (dataTaker 50).
The second command instructs the dataTaker to measure the digital byte of the signals applied to the digital input channels 1 through 3 (binary 11100) of any logger.
The DB specifies that the digital state signals applied to the digital input channels are to be read as a byte.
DeLogger does not support digital byte measurements. However the User channel type (DeLogger Version 4.2.15 or later) can be used, entering the DeTransfer commands described above.
Data from digital byte inputs is returned as a decimal value in the following ranges
dataTaker 50 - 0 to 31
dataTaker 500/600 series loggers - 0 to 15
Channel Expansion Module (CEM-AD) - 0 to 255
with units of Byte, representing the bit pattern of the status of consecutive digital input channels.
The dataTaker will read the inputs every 10 minutes, and readings are stopped by entering a H (Halt) command.