Campbell CS325DM Manuale utente

Revision: 07/2020

Campbell Scientific, Inc.

Table of contents

1. Introduction 1

2. Precautions 1

3. Initial inspection 1

4. Overview 2

5. Specifications 2

6. Siting 4

7. Mounting 4

8. Wiring 4

9. Programming 6

9.1 RS-485 programming 6

9.1.1 Register map 6

9.2 Analog programming 7

10. Maintenance and troubleshooting 8

Appendix A. Example programs 9

Table of Contents - i

1. Introduction

The CS325DM, manufactured by Atonometrics as the RC18, is a silicon solar irradiation sensor

commonly used as a reference cell in solar PV monitoring applications. The sensor element was

designed to correspond to that of a photovoltaic (PV) module, including spectral selectivity and

incident angle modifier. The data signals are Modbus RTU RS-485 or analog.

2. Precautions

lREAD AND UNDERSTAND the Safety section at the back of this manual.

lDo not remove the screws on the top cover of the CS325DM, as this may compromise the

weather-proof seal.

lTo minimize the potential for water entry to the sealed housing, mount the CS325DM with

the cable facing down or to the side.

lWhen opening the shipping package, do not damage or cut the cable jacket. If damage to

the cable is suspected, consult with a Campbell Scientific support engineer.

lAlthough rugged, the CS325DM should be handled as a precision scientific instrument.

3. Initial inspection

lUpon receipt of the CS325DM, inspect the packaging and contents for damage. File

damage claims with the shipping company.

lThe model number and cable length are printed on a label at the connection end of the

cable. Check this information against the shipping documents to ensure the expected

product and cable length were received.

CS325DM Silicon Irradiance Reference Sensor 1

4. Overview

The CS325DM is specifically designed for low-cost, high-accuracy solar irradiance measurements

for outdoor monitoring of PV systems. It includes both user-configurable analog outputs and

digital communication via Modbus (RS-485). The CS325DM includes a microprocessor that stores

the calibration data, eliminating the need to reprogram data loggers or SCADA systems when

installing a new unit.

The CS325DM measures irradiance using a crystalline silicon PV cell. The PV cell short-circuit

current is measured with a precision shunt resistor and PV cell temperature is measured with a

back-of-cell resistance temperature device (RTD).

The IP67-rated cast aluminum enclosure provides for solid mounting and protection from the

elements. The M12 circular connector allows easy installation and cable replacement.

Features

lRugged design with wide temperature operating range

lAnalog and/or digital outputs available

lSpectral selectivity and incident angle modifier correspond to crystalline PV module

lBuilt-in cell temperature measurement and signal compensation

5. Specifications

Measurement range: 0 to 1500 W/m2

Operating temperature: –35 to 80 °C

Input power: 8 to 28 VDC

Photovoltaic cell: Crystalline Si, 20 mm x 20 mm, ~135 mA @ 1 sun

Window: Low-iron solar glass, or CdTe-matching filter

Cell temperature

measurement: –40 to +100 °C, Pt100 RTD

Calibration data: Internally calibrated; no calibration data to manage

Enclosure material: Powder-coated cast aluminum housing

Enclosure outdoor rating: IP67

Cable type: Shielded, weather-resistant, UV-rated, 24 AWG/0.2 mm2

CS325DM Silicon Irradiance Reference Sensor 2

Cable connector: M12 circular connector, IP67

Response time: 0.15 s

Electronics non-linearity: ±0.03% of range

Repeatability: ±0.02% of range

Temperature drift: ±0.4% at 1000 W/m2(–35 to 80 °C)

Resolution: 0.1 W/m2

Factory calibration

of electronics: ±0.1% of reading ±0.2% of range

Irradiance calibration: ±1.2%, calibrated to NREL-traceable reference standard

Overall measurement

uncertainty: ±2.0% @ 1500 W/m2, ±2.9% @ 100 W/m2

Stability: 0.5% per year

Mounting: Four mounting holes with diameter 5.50 mm (0.217 in)

Dimensions: 11.5 x 6.5 x 3.0 cm (4.5 x 2.6 x 1.2 in)

Weight: 0.3 kg (0.6 lb)

Digital output

Communications

protocols: Modbus over RS-485, user-settable Modbus address

Baud rate: Up to 57.6 kbps

Current consumption: Typically 8 to 15 mA

Analog output

Analog output options: 0 to 1.5 V; 0 to 10 V; 4 to 20 mA

Output signals: Irradiance, cell temperature, short-circuit current

Output impedance: 2 kohm (0 to 1.5 V or 0 to 10 V mode)

Internal voltage drop: Allow 3.5 V minimum (4 to 20 mA mode)

CS325DM Silicon Irradiance Reference Sensor 3

6. Siting

A CS325DM used for monitoring PV installations must be installed with the same alignment and

inclination as the PV generator. The mounting location should be free of shading. To facilitate

maintenance and cleaning, mount the CS325DM in an easily accessible location such as near

windows or skylights.

7. Mounting

Use the CM261-LP to mount to a single axis tracker or the CM256-LP to mount the sensor at a

fixed angle.

1. Place the sensor on the top plate.

2. Use the mounting screws shipped with the sensor to secure the sensor to the top plate.

3. Using a diopter in combination with a solar compass, install and orient the crossarm on the

tripod or the mast.

4. Place the V-bracket or U-bolt on the crossarm and tighten the bolts or U-bolt nuts.

5. Use the bubble level and leveling bolts to level the sensor.

6. If using the CM256-LP, tilt to the correct azimuth and tighten bolts.

7. Verify mounting hardware is firmly tightened, and that the mounting bracket is horizontal

or at the desired angle.

8. Route the sensor cable to the enclosure.

9. Secure the cable to the crossarm and tripod or tower mast.

8. Wiring

The CS325DM outputs either a Modbus RTU RS-485 or an analog signal. Table 8-1 (p. 5) provides

the Modbus RS-485 wiring and Table 8-2 (p. 5) provides analog wiring. The RS-485 output can

be directly read by a MeteoPV, CR6, CR1000X, or Modbus RTU RS-485 network. Other Campbell

Scientific data loggers can use an MD485 multidrop interface to read the RS-485 output. Refer to

the MD485 manual for more information.

CS325DM Silicon Irradiance Reference Sensor 4

Table 8-1: RS-485 pin-out, wire color, function, and data logger connection

Wire color1Pin-out Function Data logger2connection

Blue 8 RS-485 A- A-,C(odd)

White/blue stripe 7 RS-485 B+ B+,C(even)

Brown 1 8 to 24 VDC 12V

White/brown stripe 2 Power and signal ground G

Orange 3 G ⏚(analog ground)

Green 4 G ⏚(analog ground)

Clear N/A Shield ⏚(analog ground)

1The white/orange striped and white/green striped wires are not used.

2Assumes the sensor directly connects to the data logger.

Table 8-2: Analog pin-out, wire color, function, and data logger connection

Wire color1Pin-out Function Data logger connection

White/orange

stripe 5Irradiance

input

Uconfigured for single-ended analog input2,

SE (single-ended, analog-voltage input)

White/green

stripe 6Temperature

input

Uconfigured for single-ended analog input2,

SE (single-ended, analog-voltage input)

Brown 1 8 to 24 VDC 12V

White/brown

stripe 2Power and

signal ground G

Orange 3 G ⏚(analog ground)

Green 4 G ⏚(analog ground)

Clear N/A Shield ⏚(analog ground)

1The white/blue striped and blue wires are not used.

2Uterminals are automatically configured by the measurement instruction.

CS325DM Silicon Irradiance Reference Sensor 5

9. Programming

Programming basics for CRBasic data loggers are provided in the following sections. Complete

program examples for measuring the Modbus over RS-485 and analog outputs can be found in

Example programs (p. 9). Campbell Scientific recommends using Modbus over RS-485.

9.1 RS-485 programming

The RS-485 output can be directly read by a MeteoPV, CR6-series, CR1000X-series, or Modbus

RTU RS-485 network. Other Campbell Scientific data loggers can use an MD485 multidrop

interface to read the RS-485 output. Refer to the MD485 manual for information about using the

MD485. Refer to www.campbellsci.com/videos/meteopv for information about using the

MeteoPV.

A CR6 or CR1000X data logger programmed as a Modbus Master can retrieve the values stored in

the Input Registers (Register map (p. 6)). To do this, the CRBasic program requires SerialOpen()

followed by ModbusMaster(). The SerialOpen instruction has the following syntax:

SerialOpen (ComPort, Baud, Format, TXDelay, BufferSize, Mode)

The Format parameter is typically set to logic 1 low; even parity, one stop bit, 8 data bits. The

Mode parameter should configure the ComPort as RS-485 half-duplex, transparent.

The ModbusMaster() instruction has the following syntax:

ModbusMaster (Result, ComPort, Baud, Addr, Function, Variable, Start, Length,

Tries, TimeOut, [ModbusOption])

The Addr parameter must match the sensor Modbus address. To collect all of the values, the

Start parameter needs to be 1 and the Length parameter needs to correspond with the

the CRBasic Editor Help.

9.1.1 Register map

Table 9-1 (p. 7) provides the register map for the most commonly used values. Calculated

irradiance uses the following equation:

CS325DM Silicon Irradiance Reference Sensor 6

Table 9-1: RS-485 register map

Starting register

number

count Data format Units Description

2 2 Single-precision 32 bit

floating point W/m² Calculated irradiance

4 2 Single-precision 32 bit

floating point A

Measured short-circuit

current (Isc) of the PV cell,

without temperature

correction

6 2 Single-precision 32 bit

floating point °C Measured temperature (T)

of the PV cell

105 4 Char x 2 n/a

Serial number of the unit,

up to eight characters,

two characters per register

121 5 Signed 16 bit integer n/a

Part number of the unit,

up to 10 characters, two

characters per register

9.2 Analog programming

Two VoltSE() CRBasic instructions are required to measure the analog output: one instruction

for the irradiance measurement and the other instruction for the temperature measurement.

CAUTION:

Nearby AC power lines, electric pumps, or motors can be a source of electrical noise. If the

sensor or data logger is located in an electrically noisy environment, the measurement should

be made with the 60 or 50 Hz rejection integration option as shown in the example programs.

If measurement time is not critical, the autorange option can be used in the VoltSE()

instruction; the autorange adds a few milliseconds to the measurement time. Select the smallest

input range that is greater than the maximum expected input voltage.

If electromagnetic radiation can be a problem, use an fN1 of 50 or 60 Hz. Select 60 Hz Noise

Rejection for North America and areas using 60 Hz AC voltage. Select 50 Hz Noise Rejection for

most of the Eastern Hemisphere and areas that operate at 50 Hz. The multiplier converts the

millivolt reading to engineering units.

CS325DM Silicon Irradiance Reference Sensor 7

10. Maintenance and

troubleshooting

The CS325DM should be recalibrated following industry standard best practices such as ASTM

G167, ISO 9846, ASTM E824 or ASTM G207 by an accredited lab. The recommended recalibration

interval is 2 years.

The most common reason for communication failure for the CS325DM is because the sensor is

not configured properly. Ensure that the sensor has a unique Modbus address and proper RS-485

settings.

CS325DM Silicon Irradiance Reference Sensor 8

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