DNA - Group3 DeviceNet Module
The DNA is a precision control and monitoring module that can be integrated into a DeviceNet system. It provides 16 bit resolution analog input and output capabilities, and isolated digital inputs and outputs in the same small unit.
When used with the SCM I/O board it has facilities to power up the Group3 corrected analog Hall probe, and use the signal from that as the prime input to a PID control algorithm embedded within its operating system.
The unit consists of a main circuit board contained entirely within a metal enclosure, linked by a short length of 40way ribbon cable to an I/O board mounted on top of the case. There are two possible I/O boards - the SCA which has rows of screw terminals for general I/O use, and a more specialised version - SCM - which is intended for use with the Group3 corrected analog Hall probe.
The module incorporates several features to ensure reliable operation: in addition to the checks built into the microprocessor itself there is a separate supervisor (watchdog) chip to reset the microprocessor if it detects incorrect operation as a result of an unusually powerful electrical transient. The software running within the module is of a multitasking nature, and one of the independent tasks is a dedicated self checking process that continually monitors all the other tasks and variables in the microprocessor. If anything is found to be out of normal bounds then a reset is forced.
A diagnostic port on each module allows system monitoring, configuring and debugging. The diagnostic port is invaluable at all phases of system commissioning. By using a standard terminal the engineer can access a module independently of the DeviceNet communications. A built-in menu system provides for a wide range of diagnostic, simulation, and set-up functions. A restricted access level security system prevents undesirable tampering by unauthorised personnel.
DNA Features / Specifications:
Two Analog Input channels
- 16 bit resolution, unipolar, each with differential inputs.
- Input Ranges: -10 to +10 Volt (1 lsb = 0.3mV) and
- -100 to +100mV (1 lsb = 3 m V )
- Input impedence: 94kΩ
- Both channels sampled 33 times per second.
One Analog Output channel.
- 16 bit resolution,
- Output signal selectable as: -10 to +10 volt range, (1 lsb = 0.3mV), or
- 4 to 20 mA current output. (1 lsb = 0.4 mA)
- Output impedence: 100 Ω
Eight Digital Inputs, sampled every millisecond
- The main board senses TTL level inputs on the 40 way connector.
- Inputs from sensors and switches are wired to the I/O board first, which opto-isolates the signals before passing them on to the main board.
Eight Digital Outputs, set every millisecond.
- The main board generates output signals by open drain MOSFET drivers, sinking current to digital ground. There is a 1Kohm pull up to +5V on these lines. The output drive signals are passed up to the I/O board where they are used to switch reed relays, which isolate the module from the output loads
Power supply input required to power up the isolated processing and I/O sections:
- 18 to 36 volt DC, or 14 to 26 volt (rms) AC,
- 3 Watts as simple I/O device,
- 5 Watts if used with Group3 corrected analog Hall probe.
- Connector required - Phoenix MSTB 2.5/2-ST-5.08, or Klippon equivalent.
- Unit contains an internal switch mode supply, providing isolation up to 200 volts.
- Inrush current at switch-on less than 3 amps peak, half height width of 200microseconds.
- No manual adjustments on the board - all setup and calibration is implemented by software through the diagnostic port.
DeviceNet Interface:
Communications by standard DeviceNet protocol, as a Group2 only slave.
Pre-defined Master-Slave connection set.
All values to be output from the module can be sent in one message.
All values measured by module can be read back in one message.
Module able to handle polls at 2ms intervals at 500Kbaud.
Full implementation of the "Parameter Object" - 88 instances.
Settings: - screwdriver adjustment of 10-position rotary switches, on end panel of unit.
Baud rate - rotary switch selection of 125K, 250K, 500K 10 posn, of which 0-2 are valid, remainder cause module status LED to flash red.
MAC ID
Two rotary switches, for tens and units. 10 position, valid values 0-63, remainder cause module status LED to flash red.
Indicators: on end panel of unit.
Two bicolour LEDs, for Module Status, and for Network Status, use as per ODVA spec.
Connector:
5 pin micro DeviceNet connector, right angle, male, on end panel of unit.
All I/O lines of the module are isolated from the DeviceNet signal and power lines.
Opto-couplers on data lines.
Opto-coupled bus power sense.
Current draw from bus nominal 24V is 50mA.
PID control
The module has an embedded PID control algorithm that can be invoked by sending the appropriate command, or by selecting it through the diagnostic port.
As a general I/O device, without PID, all inputs are general purpose inputs, and the value sent to the analog output is used directly to set the output voltage.
If the unit is being a controller, with PID invoked, then the value sent by the control computer to the analog output data location is the desired setting for the control variable - the setpoint.
Diagnostic Port
The Diagnostic Port, allows configuration and local control over-ride. It provides direct access to all input and output channels, with useful system diagnostic features. System set-up parameters, calibrations and resets can all be performed through this port.
Access is from a terminal with an RS-232 serial port, via an 8 pin mini-DIN socket. A small hand held terminal with an LCD screen is available from Group3. Communication is fixed at 9600bd, 7data, even parity, 2 stop bits.
All features of the diagnostic port can also be accessed over the DeviceNet network by using the "Parameter Object" implementation.
Noise Immunity
Immunity to noise and electrical transients is greatly enhanced by hardware, software and enclosure design techniques.
Several layers of isolation are employed - the DeviceNet interface is opto-isolated, the module processor and I/O sections are isolated from the local power supply by a DC to DC converter, the digital outputs are isolated by the use of relays, and the digital inputs are opto-isolated.
The power supplied to the Group3 corrected analog Hall probe is isolated by yet another DC to DC converter. The signal returned by the probe is a floating signal (with respect to its case and power supply), and is referenced to the level of analog input 0 of the controller.
Two stage transient suppression -all I/O pins on the main controller board have fast acting, voltage limiting components installed, and further suppression and isolation components are on the I/O board.
Particular attention has been paid to hardware design for minimal noise susceptibility - good grounding and decoupling layout, minimising signal lengths and areas, and inclusion of hardware watchdog circuitry.
Robust embedded software.
Self diagnosing and fault tolerant software allows graceful recovery after a disturbance caused by a transient. The unit is continually running self checks on its operating state - if anything is found to be out of allowed limits the microprocessor can recover to a known good state without operator intervention.
The case is of an all metal design, providing the best EMI shielding.
I/O Board - SCA & SCM - Features / Specifications:
These boards provide additional transient protection and/or isolation on all I/O channels.
Most of the circuitry is common to both boards, in particular the suppression and voltage division on the analog channels, and the configurable input types on the digital inputs.
Eight Digital Inputs, sampled every millisecond
- The main board senses TTL level inputs on the 40 way connector. Inputs from sensors and switches are wired to the I/O board first, which opto-isolates the signals before passing them on to the main board.
- Opto-couplers on each channel can be selected to operate in two possible modes:
- Signal powered channels are completely independent, minimum of 5mA
- Contact closure channels share a common return potential (which is isolated from the rest of the unit up to 500V)
Eight Digital Outputs, set every millisecond.
- Small reed relay contacts, Switching 100 volt, 500mA maximum.
- Max. switched power - 10W
- Isolation of contacts from rest of unit - 300 volts
SCA I/O board
The SCA board provides rows of screw terminals to allow easy field wiring to each I/O channel.
Each digital input channel, and each digital output channel has a three position screw terminal associated with it. Each of the analog channels has a four position terminal block of 3.81mm pitch.
SCM I/O board
I/O signals are brought into the module by way of vertical mount female D-sub connectors.
Different connectors are used for each grouping of signals, in part to avoid the possibility of mis-connecting in the field.
Physical Details
Connectors
- Between the boards - 40 pin dual row 0.1" spacing boxed header on main board
- 40 way ribbon cable with matching socket attached to I/O board.
- Diagnostic Port - 8 way miniDIN round socket.
DeviceNet power and data connector - sealed micro style, right angle male.
Module power - Phoenix MSTB 2.5/2-ST-5.08, or Klippon equivalent.
Case.
- Aluminium extrusion 140 x 92 x 29 mm
- Stainless steel endplates with integral DIN rail locking system.
Mounting.
- Stainless Steel DIN rail clamp is integral to the metalwork of the unit.