Campbell 3WHB10K Manual de usuario

Revision:03/2020

Campbell Scientific, Inc.

Table of contents

1. Function 1

2. Specifications 2

3. Wiring 2

4. Programming examples 4

4.1 GRANITE 9/10 program example 5

4.2 GRANITE 6/CR6 program example 6

4.3 CR1000X program example 6

4.4 CR1000 program example 7

4.5 CR9000X program example 7

5. 100 Ohm PRT in 3-wire half bridge 8

5.1 Excitation voltage 8

5.2 Calibrating a PRT 9

5.3 Compensation for wire resistance 9

Table of Contents - i

1. Function

A terminal input module (TIM) connects directly to a data logger or GRANITE analog input

module. It provides completion resistors for resistive bridge measurements, voltage dividers, and

precision current shunts. The 3WHB10k is used in 3-wire half bridge measurements and includes

a 10 kΩ completion resistor.

NOTE:

The GRANITE 6 and CR6 include the fixed resistor and current excitation required to complete

the half-bridge circuit without a terminal input module. However, the GRANITE 6 and CR6

are still compatible with a terminal input module and may be used with one, should the

application require it.

FIGURE 1-1. Terminal input module

3WHB10K 3-Wire Half Bridge Terminal Input Module 1

2. Specifications

10 kΩ completion resistor

Tolerance @ 25 °C: ±0.01%

Maximum temperature

coefficient

±0.8 ppm/°C

Power rating @ 70 °C: 0.25 W

EU certificate of conformity: https://s.campbellsci.com/documents/us/compliance/eudoc_

terminal-input-modules.pdf

FIGURE 2-1. Schematic

3. Wiring

The terminal input module is connected to adjacent Hand Lterminals. When making 3-wire half

bridge measurements, the 3WHB10K performs two single-ended measurements. The sense wires

from the platinum resistance thermometer (PRT) attach to the 3WHB10K. The black excitation

wire is connected to an excitation terminal. In the following example, the 3WHB10K is connected

to the 1H and 1L terminals, using them for two single-ended measurements. The excitation wire is

connected to excitation terminal VX1 (FIGURE 3-1 (p. 3)).

3WHB10K 3-Wire Half Bridge Terminal Input Module 2

Often, sensors only have two wires. Use the 3WHB10K as a fixed, known resistor to measure them.

Wire a jumper between the Hand Lterminals on the 3WHB10K to allow the sensor to receive

excitation voltage. Without the jumper, the sensor will not function. See FIGURE 3-1 (p. 3).

When using a 2-wire sensor with the 3WHB10K, use the BrHalf() (or CDM_BrHalf())

instruction in place of the BrHalf3W() (or CDM_BrHalf3W()) instruction. The parameters of

the BrHalf3W() and BrHalf() instructions are identical; so, only the instruction name

needs to be changed in the Programming examples (p. 4) example programs.

FIGURE 3-1. 3-wire half bridge used to measure PRT

The terminal spacing of the GRANITE 6 and GRANITE analog input module is different than

other data loggers. The terminal input modules are still compatible, but the pins must be gently

bent inward a small amount to allow the terminal input module to be mounted.

It is still possible to use terminal input modules in adjacent terminal blocks if the modules are

staggered. This is done by gently bending one module forward and the next terminal backward

enough to clear the first module. Continue to alternate the modules as needed.

3WHB10K 3-Wire Half Bridge Terminal Input Module 3

Table 3-1: 3WHB10K connections to Campbell Scientific data loggers

Function Label/Wire

GRANITE

analog input

module

GRANITE6,

CR6

CR3000,

CR1000X,

CR800, CR850,

CR1000

CR9000X

Excitation Black wire X1 U5 VX1 Excitation 1

V1 high

reference H 1H U1 1H 1H

V1 low sense L 1L U2 1L 1L

Ground G ⏚ ⏚ ⏚ ⏚

1The GRANITE 9 and GRANITE 10 do not directly make analog measurements. Instead, they use analog input

modules such as the VOLT 108 or VOLT 116. When making a half-bridge measurement, the terminal input module is

connected to the analog input module, which is then connected to the GRANITE 9 or GRANITE 10.

4. Programming examples

The following examples show the two instructions necessary to 1) make the measurement and 2)

calculate the temperature. The result of the half bridge measurement as shown is Rs/R0, the input

required for the PRT algorithm to calculate temperature.

If using a calibrated sensor, the exact measurement of R0will be known. Use this value to

increase the accuracy of the PRTCalc() instruction by inserting the following equation

between the BrHalf4W() and PRTCalc() instructions in the example programs.

Rs_R0 = Rs_R0*100/R0

where R0 is the sensor resistance at 0 °C

The following examples are based on a maximum sensor resistance of 100 Ω at 0 °C. The

excitation voltages used were chosen with the assumption that the temperature would not

exceed 50 °C. Calculation of optimum excitation voltage is discussed in Excitation voltage (p. 8).

3WHB10K 3-Wire Half Bridge Terminal Input Module 4

4.1 GRANITE 9/10 program example

The GRANITE9 and GRANITE10 require the use of an analog input module, such as the

VOLT108, when making a half-bridge measurement.

CRBasic Example 1: GRANITE9/10 3-wire half bridge example

'3-wire half bridge example

'GRANITE 9 and GRANITE 10 data loggers (with a VOLT 108)

'Declare Variables and Units

Public Temp_C_3wire

Public Rs_R0

'Define Data Tables

DataTable(Hourly,True,-1)

DataInterval(0,60,Min,10)

Average(1,Temp_C_3wire,IEEE4,False)

EndTable

'Main Program

BeginProg

'Configure the VOLT 108 Module and assign it CPI address 'CPI_BUSA+1'

CPIAddModule(VOLT108,10," ",CPI_BUSA+1)

'Main Scan

Scan(5,Sec,1,0)

'Half Bridge, 3-wire measurements on the VOLT 108

CDM_BrHalf3W(VOLT108,CPI_BUSA+1,Rs_R0,1,mV1000,1,1,1,3200,True,500,60,1,0)

'PRT temperature calculation

PRTCalc (Temp_C_3wire,1,Rs_R0,0,1.0,0)

'Call Data Tables and Store Data

CallTable Hourly

NextScan

EndProg

3WHB10K 3-Wire Half Bridge Terminal Input Module 5

4.2 GRANITE 6/CR6 program example

The GRANITE 6 and CR6 include the fixed resistor and current excitation required to complete

the half-bridge circuit without a terminal input module. However, the GRANITE 6 and CR6 are

still compatible with a terminal input module and may be used with one, should the application

require it.

CRBasic Example 2: GRANITE 6/CR6 3-wire half bridge example

'GRANITE 6/CR6 data logger 3-wire half bridge using a terminal input module

Public Rs_R0, Temp_C

DataTable (Hourly,True,-1)

DataInterval (0,60,Min,0)

Average (1,Temp_C,IEEE4,0)

EndTable

BeginProg

Scan (1,Sec,0,0)

BrHalf3W (Rs_R0,1,mV1000,U1,U4,1,2500,True ,0,250,100,0)

PRTCalc (Temp_C,1,Rs_R0,0,1,0)

CallTable Hourly

NextScan

EndProg

4.3 CR1000X program example

CRBasic Example 3: CR1000X 3-wire half bridge example

'CR1000X-series data logger 3-wire half bridge

Public Rs_R0, Temp_C

DataTable (Hourly,True,-1)

DataInterval (0,60,Min,0)

Average (1,Temp_C,IEEE4,0)

EndTable

BeginProg

Scan (1,Sec,0,0)

BrHalf3W (Rs_R0,1,mV1000,1,Vx1,1,3200,True ,0,250,100,0)

PRTCalc (Temp_C,1,Rs_R0,0,1,0)

CallTable Hourly

NextScan

EndProg

3WHB10K 3-Wire Half Bridge Terminal Input Module 6

4.4 CR1000 program example

CRBasic Example 4: CR1000 3-wire half bridge example

'CR1000-series data logger 3-wire half bridge

Public Rs_R0, Temp_C

DataTable (Hourly,True,-1)

DataInterval (0,60,Min,0)

Average (1,Temp_C,IEEE4,0)

EndTable

BeginProg

Scan (1,Sec,0,0)

BrHalf3W (Rs_R0,1,mV2500,1,Vx1,1,2500,True,0,250,100,0)

PRTCalc (Temp_C,1,Rs_R0,0,1,0)

CallTable Hourly

NextScan

EndProg

4.5 CR9000X program example

CRBasic Example 5: CR9000X 3-wire half bridge example

'CR9000X data logger 3-wire half bridge

Public Rs_Ro, Temp_F

DataTable (Temp_F,1,-1)

DataInterval (0,60,Min,0)

Sample (1,Temp_F,FP2)

EndTable

BeginProg

Scan (1,mSec,0,0)

BrHalf3W (RS_Ro,1,mV1000,5,1,6,1,1,3200,True,30,40,100,0)

PRTCalc (Temp_F,1,Rs_Ro,0,1.8,32)

CallTable Temp_F

NextScan

EndProg

3WHB10K 3-Wire Half Bridge Terminal Input Module 7

5. 100 Ohm PRT in 3-wire half

bridge

The advantages of the 3-wire half bridge over other measurements that correct for wire resistance

such as a 4-wire half bridge, are that it only requires 3 wires going to the sensor and takes 2

single-ended terminals, whereas the 4-wire half bridge requires 4 wires and 2 differential

channels.

The result of the 3-wire half bridge instruction is equivalent to the ratio of the PRT resistance, Rs

to the resistance of the 10k fixed resistor, Rf.

The PRTCalc() instruction computes the temperature (°C) for a DIN 43760 standard PRT from

the ratio of the PRT resistance at the temperature being measured (Rs) to its resistance at 0°C

(R0). Thus, a multiplier of Rf/R0is used with the 3-wire half bridge instruction to obtain the

desired intermediate, Rs/R0= (Rs/Rfx Rf/R0). If Rfand R0are equal, the multiplier is 1.

The fixed resistor must be thermally stable. The 0.8ppm/°C temperature coefficient would result

in a maximum error of 0.035°C at 125°C. This measurement is ratiometric (Rs/Rf) and does not

rely on the absolute values of either Rsor Rf.

The properties of the 10 kΩ resistor do not affect the result. The purpose of this resistor in the

circuit is to limit current.

5.1 Excitation voltage

When determining the excitation voltage, it is important to consider the maximum excitation

current the sensor can experience without self-heating. This is typically less than 35 mA. Refer to

the manufacturer's data sheet for the sensor for the specific value.

Once the maximum excitation current is known, the excitation voltage is then calculated.

Vx= Ix(Rf+ RSmax)

Where:

Rf= PRT completion resistor value

3WHB10K 3-Wire Half Bridge Terminal Input Module 8

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