Winson MH-Z14A Intelligent Infrared Carbon Dioxide Module User Manual
- June 5, 2024
- WINSON
Table of Contents
Winson MH-Z14A Intelligent Infrared Carbon Dioxide Module
Profile
MH-Z14A NDIR Infrared gas module is a common type, small size sensor, using non-dispersive infrared (NDIR) principle to detect the existence of CO2 in the air, with good selectivity, non-oxygen dependent and long life. Built-in temperature sensor can do temperature compensation; and it has digital output and PWM output. This common type infrared gas sensor is developed by the tight integration of mature infrared absorbing gas detection technology, Precision optical circuit design and superior circuit design.
Main Features
- Chamber is gold plated, water-proof and anti-corrosion High sensitivity, low power consumption
- Good stability
- Temperature compensation, excellent linear output Multiple output modes: UART, PWM
- Long lifespan
- Anti-water vapor interference, anti-poisoning
Applications
- HVAC refrigeration
- Smart home
- Air cleaner device
- Ventilation system
- Indoor air quality monitoring
Main technical parameters
| Model No. | MH-Z14A |
|---|---|
| Detection Gas | CO2 gas |
| Working voltage | DC (5.0±0.1V) |
| Average current | < 40 mA (@5V supply) |
| Peak current | 125mA (@5V supply) |
| Interface level | 3.3 V (5V compatible) |
| Measuring range | 400~10000ppm optional |
Output signal
| Serial port(UART) (TTL)
PWM
Preheat time| 1min
Response Time| T90 < 120s
Working temperature| -10℃ ~ 50℃
Working humidity| 0~95%RH(no condensation)
Storage temperature| -20℃ ~ 60℃
Weight| 14 g
Lifespan| >10 years
Target Gas| Measuring Range| Resolution| Accuracy
---|---|---|---
Carbon Dioxide (CO2)| 400~2000ppm| 1ppm| ±(50ppm
+5%reading value)
400~5000ppm
400~10000ppm
Structure
Definition for pins
| PIN No | Description |
|---|---|
| 1,15,23 | Power positive (Vin) |
| 2,3,12, 22 | Power negative (GND) |
| 4,5,21 | NC |
| 6,26 | PWM |
| 8, 20 | HD(for zero-point calibration, low level lasting for |
over 7 sec is effective)
7,9| NC
11, 14, 24| UART（RXD） TTL data input
10,13, 25| UART（TXD）TTL data output
Two Output ways
PWM output
Take 400~2000ppm for example
CO2 output range| 400~2000ppm
Cycle| 1004ms±5%
Cycle start high level output| 2ms(theoretical value)
The middle cycle| 1000ms±5%
cycle end low level output| 2ms(theoretical value)
CO2 concentration: Cppm=2000×(TH -2ms)/(TH+TL-4ms)
Cppm: CO2 concentration could be calculated by PWM output TH high level output
time during cycle
TL low level output time during cycle
Serial port output (UART)
Hardware connection
Connect module’s Vin-GND-RXD-TXD to users’ 5V-GND-TXD-RXD. (Users must use TTL
level. If RS232 level, it must be converted.)
Software setting
Set serial port baud rate be 9600, data bit 8 bytes, stop bit 1byte, parity
bit null.
Command List:
| 0x86 | Gas concentration |
|---|---|
| 0x87 | Calibrate zero point（ZERO） |
| 0x88 | Calibrate span point（SPAN） |
| 0x79 | ON/OFF Self-calibration function for zero point |
| 0x99 | Detection range setting |
0x86- Read CO2 concentration
Sending command
Byte0| Byte1| Byte2| Byte3| Byte4| Byte5| Byte6| Byte7| Byte8
Start Byte| Reserved| Command| –| –| –| –| –| Checksum
0xFF| 0x01| 0x86| 0x00| 0x00| 0x00| 0x00| 0x00| 0x79
Return value
Byte0| Byte1| Byte2| Byte3| Byte4| Byte5| Byte6| Byte7| Byte8
Start Byte| Command| Concentration
(High 8 Byte)
| Concentration
(Low 8 Byte)
| –| –| –| –| Checksum
0xFF| 0x86| HIGH| LOW| –| –| –| –| Checksum
*CO2 concentration = HIGH 256 + LOW For example:**
Send command FF 01 86 00 00 00 00 00 79, Return value FF 86 02 20 00 00 00 00 58
*How to calculate concentration: convert hexadecimal 02 into decimal 2, hexadecimal 20 into decimal 32, then 2256+32=544ppm**
0x79- On/Off Self-calibration for Zero Point
Send command-No return value
Byte0| Byte1| Byte2| Byte3| Byte4| Byte5| Byte6| Byte7| Byte8
Start Byte| Reserved| Command| –| –| –| –| –| Checksum
0xFF| 0x01| 0x79| 0xA0/0x00| 0x00| 0x00| 0x00| 0x00| Checksum
For example:
ON this function, send command: FF 01 79 A0 00 00 00 00 E6
OFF this function, send command: FF 01 79 00 00 00 00 00 86
NOTE: This function is on when Byte3 is 0xA0 while this function is off when Byte3 is 0x00. Default status is “this function is on”.
1. Checksum calculation method
Checksum = (Negative (Byte1+Byte2+Byte3+Byte4+Byte5+Byte6+Byte7))+1
For example:
Byte0| Byte1| Byte2| Byte3| Byte4| Byte5| Byte6| Byte7| Byte8
Start Byte| Reserved| Comman
d
| –| –| –| –| –| Check
sum
0xFF| 0x01| 0x86| 0x00| 0x00| 0x00| 0x00| 0x00| Check
sum
Calculating Checksum：
1、Add Byte 1 to Byte 7: 0x01 + 0x86 + 0x00 + 0x00 + 0x00 + 0x00 + 0x00 = 0x87 2、Negative: 0xFF – 0x87 = 0x78
3、Then+1：0x78 + 0x01 = 0x79
C language
char getCheckSum(char *packet)
{
char i, checksum; for( i = 1; i < 8; i++)
{
checksum += packet[i];
}
checksum = 0xff – checksum; checksum += 1;
return checksum;
}
Zero Point Calibration
About zero point calibration
This module has three methods for zero point calibration: hand-operated
method, sending command method and self-calibration. All the zero point is at
400ppm CO2.
Hand-operated method: Connect module’s HD pin to low level(0V), lasting for 7
seconds at least. Before calibrating the zero point, please ensure that the
sensor is stable for more than 20 minutes at 400ppm ambient environment.
Sending command method
Zero and Span point calibration can be achieved by sending a calibration
command to the sensor via the serial port (URAT). Zero and SPAN point
calibration commands are as follows:
Self-calibration
After the module works for some time, it can judge the zero point
intelligently and do the zero calibration automatically. The calibration cycle
is every 24 hours since the module is power on. The zero point is 400ppm. This
method is suitable for office and home environment, not suitable for
agriculture greenhouse, farm, refrigerator, etc.. If the module is used in
latter environment, please turn off this function.
Notes
- Please avoid the pressure of its gilded plastic chamber from any direction, during welding, installation, and use.
- When placed in small space, the space should be well ventilated, especially for diffusion window.
- The module should be away from heat, and avoid direct sunlight or other heat radiation.
- The module should be calibrated termly, the suggested period is not longer than 6 months.
- Do not use the sensor in the high dusty environment for long time.
- To ensure the normal work, the power supply must be among 4.5V~5.5V DC rang, the power current must be not less than 150mA. Out of this range, it will result in the failure of the sensor. (The concentration output is low, or the sensor can not work normally.)
- During the zero point calibration procedure by manual, the sensor must work in stable gas environment (400ppm) for over 20 minutes. Connect the HD pin to low level (0V) for over 7 seconds.
Zhengzhou Winsen Electronics Technology Co., Ltd
Add: No.299, Jinsuo Road, National Hi-Tech Zone,
Zhengzhou 450001 China
Tel: +86-371-67169097/67169670
Fax: +86-371-60932988
E-mail: [email protected]
Website: www.winsen-sensor.com