The DSP chip has two off 10-bit A/D converters with individual built-in Sample and Hold circuits. Eight analog inputs are provided for each ADC through 8 to 1 analog multiplexers. This enables two input channels, one on each ADC, to be simultaneously sampled and converted. The maximum total conversion time for each ADC unit is 6.6ms.
The DSP A/D converters accept input voltages in the range of 0-5V. The analog inputs are interfaced as 2 off AC currents, 2 off AC voltages, 1 off DC voltage, 1 off temperature sensor, 2 off potentiometers and 2 off ±10V general purpose inputs. The AC current inputs require the placement of burden resistors (R17, R18) on the card, selected so that the full-scale voltage developed across each resistor ranges between ±550mV. Standoffs are provided on-card for ease of mounting these resistors. If required, capacitors (C9, C10) can be added in parallel with the sense resistors to reduce unwanted high frequency noise. Separate grounds are provided on each current connector so that each current input can be connected using individual twisted pair wires.
A common overcurrent detection is provided for both AC current inputs, with the trip level determined by resistor R112 (mounted on standoffs). The AC voltage inputs have a default input voltage range of ±750V peak. This can be reduced by mounting gain resistors (R23, R25, R27) onto standoffs on the PCB. The two AC voltage inputs are differential high impedance circuits, allowing the line-line AC voltages to be measured from a three phase system. One input voltage (Vab) supports a zero crossing detect circuit, which drives a DSP capture input. The DC voltage input has a default input voltage range of 928V. This can be reduced by mounting gain resistors (R41, R44) onto standoffs on the PCB. The DC voltage input is a differential high impedance circuit, allowing the DC voltage to be measured between two floating rails.
A DC overvoltage detection circuit is provided for this input, with the trip level determined by resistor R111 (mounted on standoffs). The temperature sense input supports temperature measurement using a RTD or LM35DZ temperature sensing device. A 1.0mA current source can be linked (LK5) to develop the sense voltage across the RTD. The offset and gain of the temperature sense system can be varied by changing resistors R64, R67. The potentiometer inputs can be link selected (LK3, LK4) to use either on-card trimpots, or an external potentiometer located off-card. A 5V reference voltage is available at the potentiometer connector to energize an external potentiometer. The two general purpose analog inputs accept a ±10V input. Each input has a 1 megohm resistor connected to ground to stabilize the DC level.
Hiç yorum yok:
Yorum Gönder