The PMDAIO module is a multipurpose combination of inputs and outputs. The module can accommodate either 2 or 3 wire RTD sensors, current (0-20mA) and voltage (0-10V) inputs, current (0-20mA) or voltage (0-10V) output, and digital inputs and outputs.
There are 2 RTD inputs on the module. The RTD resistance is read by the module circuitry, linearised and converted to degrees Centigrade. No ranging is required as the module covers the full range of the RTD as indicated in the RTD table. The value that is read from the Modbus register is the actual temperature in degrees centigrade to 0.1 C resolution. ie: a value of 3451 corresponds to a temperature of 345.1 C.
The Analog Inputs (2) can be configured by internal jumpers as either a current input (0-20mA) or a voltage input (0-10V).
An input of 0 - 20mA input current or 0 - 10V input voltage represents an output value of 0 - 4095 (12 bits) in the corresponding Modbus register.
There is a single analog output which can be configured with internal jumpers for a current output (0-20mA) or voltage output (0-10V).
The resolution is 12 bits, so writing a value to the Modbus register for each output of 0 - 4095 would give an output current of 0 - 20mA. A value of 819 +/- 1LSB will give a current output of 4mA.
There are 4 digital inputs on the module. The inputs share a common terminal and can be configured for common positive or common negative.
The inputs have got counters associated with them. The counters operate in three modes.
In mode 0 all the counters are disabled.
In mode 1 all counters are 32 bit counters allowing a count value from 0 to 4294967295. The count value can be cleared by writing a zero to the associated registers or preset to any other value using the same method.
In mode 2 the inputs are connected as up/down counters. Input 1 will increment counter 1 whilst input 2 decrements counter1.
Note: The count values are not battery backed-up and will be lost if power is turned off.
The format of the registers allows the status of the inputs to be read as either single bits or all at once as a single register on the Modbus network.
The module has 2 open collector (NPN) digital outputs. The outputs may be used to drive lamps or external relays when more drive capability is required.
The outputs are written to by the Modbus master device such as a PC or PLC. Each output can be individually switched on or off, or all outputs can be set up at the same time by writing a single number to the output register which represents the status of all outputs.
An output watchdog timer can be configured to switch off all the outputs if there has been no communications with the module for up to 255 seconds. A value of 0 seconds will disable this timer and the outputs will remain in the last programmed state.
SCADA software for people with other jobs!