Nokeval HTB230 2 Wire Transmitters Signal Converter and Isolator User Manual
- June 5, 2024
- Nokeval
Table of Contents
Nokeval HTB230 2 Wire Transmitters Signal Converter and Isolator
INTRODUCTION
Nokeval HTB230 is a basic level in-head transmitter for RTD sensors. The range and sensor type are programmable using an USB connected programming unit HTBPROG. The sensor repertoire includes any Pt, Ni, or Cu sensor. Also bare ohms can be measured, e.g. a potentiometer resistance. The sensor may be connected with either three or four wire connection. The transmitter has exceptionally fast start-up. After the power is applied, it takes 1.5 seconds to settle the output completely.
SPECIFICATIONS
INSTALLING
Connections
RTD sensors
Two-wire sensor is connecterd in terminals 2 and 4, and terminal 3 is linked
to terminal 2. In three-wire connection, two wires are connected in terminals
2 and 3 (usually red) and one wire in terminal 4 (white). Four-wire connection
includes connecting the fourth wire in terminal 5.
mV input
This transmitter is not intended for mV signals, but has a non-calibrated mV
input for special purposes. The signal is brought in terminals 2- and 3+.
Configuration
The software settings can be made using a separate programming unit HTB-PROG that has a USB connection to the PC.
- Connect the crocodile clips to the transmitter poles 1 (black) and 6 (red). It is recommended to disconnect the transmitter for any other current loop during the configuration. A sensor may retain connected.
- Use Nokeval Mekuwin software, available from www.nokeval.com.
- Select the HTBPROG port, 9600 baud, SCL protocol, and address 0. Click Direct.
- Change the settings and use the Mon(itor) menu.
- Click Save to EEPROM.
- Close the Mekuwin connection and disconnect the clips.
OPERATION
Measurement system
The transmitter feeds a continuous current through the sensor from connector 4
to connector 2. There is an internal 10 kohm resistor in series with the
sensor, and these are supplied with a 2.5 V voltage, to form about 250 µA
sensor current. The transmitter measures the voltage over the sensor, the
series resistor and over the other sensor wires. Some calculations are
performed to calculate the sensor resistance. In addition, a weak current of
about 5 µA is intermittently fed to the non-current carrying sensor wires to
check their condition. The resistance is converted to a temperature reading
using polynomial function. This measured temperature can be observed in the
Monitor menu item Mea.
Scaling
The user is provided a possibility to correct or scale the measured reading
using one or two points. One-point correction can be used to cancel a small
sensor error. Enter the wrong reading (seen in Monitor menu Mea) in Mea1 and
the correct reading in Sca1. Now on, the transmitter will apply an offset
correction of Sca1-Mea1. The corrected reading can be seen in Monitor menu
Sca. The same applies for two-point correction or scaling. Measurement result
Mea1 is converted to Sca1 and Mea2 to Sca2. A linear interpolation/-
extrapolation is used. These can be used to perform a two-point sensor
calibration or to scale e.g. potentiometer endpoints to show a real angle or
position
Analog output
The output is formed from the scaled or correcte reading Sca. In the Out
settings, scaled readings corresponding to 4 and 20 mA output are set.
Beginning from firmware V1.3, the output obeys the NAMUR NE43 convention:
without fault, the output is limited between 3.8 and 20.5 mA. During a fault,
it behaves according to the Out/Fault setting.
Monitoring
Some of the internal readings can be observed using the Monitor function in
the configuration program. Mea is the un-corrected reading, Sca is the user
corrected/scaled reading, and Out is the current analog output value in
milliamps.
Simulation
The transmitter provides means to test the scaling and output operation using
simulated values. The simulation is started by giving a Lock command for any
item in the Monitor menu. This is done by clicking the small L button in
Mekuwin and then entering the desired simulated value.
Mea
Simulating Mea reading can be used to see how the user scaling (Sca) works.
Sca
Simulating Sca reading can be used to see the output current and the actual
output change.
Out
Simulating the Out item means giving the analog output current in milliamps.
SETTINGS
Menu tree
The configuration menu is divided in In and Out submenus. In menu is used to configure the sensor type and other input related settings. Out menu is used to scale the analog output.
In submenu
Sensor
Sensor type. See also R0.
- Pt: Platinum RTD sensor, resul in °C.
- Ni: Nickel RTD sensor.
- Cu: Copper RTD sensor.
- ohm: Resistance measurement, in ohms.
- mV: Millivolt measurement 0-2500 mV, not very precise.
R0
Resistance of the sensor at 0°C (or at 25° with Cu sensor). E.g. with Pt100
set to 100. If the precise resistance of the sensor is known, it can be
entered here (e.g. 99.83 ohms).
4W
Four-wire measurement selection.
- No: 3-wire.
- Yes: 4-wire.
Lopass
Lowpass filter to attenuate noise and disturbances. Set time constant (63%) in
seconds, 0 to disable.
Pts
Number of correction/scaling points.
- 0: No scaling or correction. Sca reading is equal to Mea reading.
- 1: offset correction. Measured reading in Mea1 is converted to correspond to Sca1 by adding Sca1-Mea to every measurement result.
- 2: two-point correction. Reading Mea1 corresponds to corrected reading Sca1 and Mea2 corresponds to Sca2.
Mea1, Sca1, Mea2, Sca2
Scaling or correction points, see Pts. The current measured reading can be
copied to Mea1 or Mea2 by giving the Lock command in the configuration
program, and then the correct reading entered in Sca1 or Sca2.
Out submenu
Lo
Scaled reading (Sca), that corresponds to output =of 4 mA.
Hi
Scaled reading (Sca), that corresponds to output of 20 mA.
Fault
The output during sensor or other fault.
- Dscale: driven to 3.5 mA.
- Uscale: driven to 23 mA.
- Custom: driven to a user selectable current, see below. Available beginning from firmware V1.3.
Fault curr
Output current during sensor or other fault. Applies only when the previous
setting has been set to Custom. The setting can be set to any value, but the
hardware limits the actual current to approx. 3 to 24 mA.