PeterH_DK
Member
I have set up some polling devices in retail shops using a PLC ( Trilogy T100MD888) and a GSM modem to transmit data.
It works fine, but the customers would also like to count how many people enter the shops. At first I installed a Through-beam photoelectric sensor from SICKin front od the door, and divided the counted pulses by two assuming that everybody who enters also exits. This has worked for three months but required frequent attention because either the light beam or the reflector were bumped into by customers and thus got out of line and failed to count..
I therefore tried with a small PIR sensor from Parallax. The sensor is mounted in a 10cm long tube with a rectangular hole of about 2 * 8 cm and hangs from the ceiling over the entry door. It therefore only detects movement in the doorway.
In order to detect the reliability I mounted both sensors in one shop and could see that at the end of each day the registered amount of visitors was almost identical, the difference in counting was less than 3%. At first I was very happy: 3% is fine. We are not looking for a high accuracy like we could get with a Video camera – rather for a very cheap solution, that can indicate the customer flow per hour in the shops.
But when I analyze the actual counting I see a difference between the two counting methods. It levels out during the day - sometime one sensor registers more, sometimes the other.
I have reduced the counting resolution in order to save space. I have done this by counting the sensor pulses and then writing them to memory with a timestamp every time somebody votes on the polling device. This means I only know how many customers entered since the last vote. The resolution is acceptable because I collect 2-300 votes per day corresponding to approx 20% of the customers entering the shop.
But seeing the difference in measurement from the two devices it is clear that I do not count everybody who enters the shop and there are several reasons for this.
Firstly if two people walk in hand-in-hand, or two people enter and exit at the same time, that will only generate one pulse. Or if somebody stops in the doorway counting is blocked for as long as he or she is there.
So I am definitely registering less people than have actually have entered.
The question how much less? I have contemplated standing there for a couple of hours and manually registering how many entered the shop. I would then be able to estimate how many I missed
But before I stand there being totally bored for several hours I would like to hear if any of you could recommend a different and cost effective way of measuring how many people enter a shop on an hourly basis. Cost and ease of installation are both important issues. So cameras are out. But is there a better way?
/Peter
It works fine, but the customers would also like to count how many people enter the shops. At first I installed a Through-beam photoelectric sensor from SICKin front od the door, and divided the counted pulses by two assuming that everybody who enters also exits. This has worked for three months but required frequent attention because either the light beam or the reflector were bumped into by customers and thus got out of line and failed to count..
I therefore tried with a small PIR sensor from Parallax. The sensor is mounted in a 10cm long tube with a rectangular hole of about 2 * 8 cm and hangs from the ceiling over the entry door. It therefore only detects movement in the doorway.
In order to detect the reliability I mounted both sensors in one shop and could see that at the end of each day the registered amount of visitors was almost identical, the difference in counting was less than 3%. At first I was very happy: 3% is fine. We are not looking for a high accuracy like we could get with a Video camera – rather for a very cheap solution, that can indicate the customer flow per hour in the shops.
But when I analyze the actual counting I see a difference between the two counting methods. It levels out during the day - sometime one sensor registers more, sometimes the other.
I have reduced the counting resolution in order to save space. I have done this by counting the sensor pulses and then writing them to memory with a timestamp every time somebody votes on the polling device. This means I only know how many customers entered since the last vote. The resolution is acceptable because I collect 2-300 votes per day corresponding to approx 20% of the customers entering the shop.
But seeing the difference in measurement from the two devices it is clear that I do not count everybody who enters the shop and there are several reasons for this.
Firstly if two people walk in hand-in-hand, or two people enter and exit at the same time, that will only generate one pulse. Or if somebody stops in the doorway counting is blocked for as long as he or she is there.
So I am definitely registering less people than have actually have entered.
The question how much less? I have contemplated standing there for a couple of hours and manually registering how many entered the shop. I would then be able to estimate how many I missed
But before I stand there being totally bored for several hours I would like to hear if any of you could recommend a different and cost effective way of measuring how many people enter a shop on an hourly basis. Cost and ease of installation are both important issues. So cameras are out. But is there a better way?
/Peter