You will be charged Rs.15 plus service tax for each scrip, per day on date of selling whenever you sell a scrip on a delivery basis.
Ex: You are selling delivery shares of SBI 100 qty on Monday at 10am, 50 qty at 11am, 10 qty at 2pm. You will be charged Rs.15+service tax of demat transaction charge for SBI scrip. On same day if you sell any other stock with any quantity, you will be charged again Rs.15 demat transaction charge. Totally, you sold 2 stocks(scrips), hence you are required to pay Rs.30.